Binder system and method for particulate material cross-reference to related application

ABSTRACT

The present invention relates to a binder composition comprising an aliphatic polyester polymer: an ethylenebisamide wax; and a guanidine wetting agent. The composition may also contain an additive which accelerates or extends debinding of the binder composition, and to a method for forming a sintered part by powder injection molding, including the steps of forming a green composition comprising a binder and an inorganic powder, wherein the binder is a composition comprising an aliphatic polyester polymer, an ethylenebisamide wax, and a guanidine wetting agent, and may further include an additive which accelerates or delays completion of debinding of the binder; melting the composition; injecting the composition into a mold for a part; heating the part to a temperature at which the binder decomposes; heating the part to a temperature at which the inorganic powder is sintered.

This application is a 371 of PCT/US01/20141 filed Jun. 22, 2001, whichis a continuation-in-part of and claims priority under 35 U.S.C. §120 toU.S. application Ser. No. 09/603,678, filed Jun. 26, 2000 now U.S. Pat.No. 6,376,585.

FIELD OF THE INVENTION

The present invention relates to binder compositions for use in formingsintered parts by powder injection molding and to green compositionscontaining the binder composition and inorganic powders and to methodsof reverse debinding using the binder and green compositions. In oneembodiment the binder compositions may include additional componentswhich provide a broader range of control of reverse debinding, and tomethods of using such binder compositions. The binders of the presentinvention require fewer steps to produce a part have higher thixotropicenergy, and melt at a lower temperature than traditional binders forPIM. The binder compositions provide a green body having high strength,and decompose thermally in a clean, substantially ash-free burnout toyield simple, environmentally safe decomposition products. In oneembodiment, the binder composition may further include additives bywhich the rate and temperatures of debinding may be selected andcontrolled.

BACKGROUND OF THE INVENTION

Processes for forming shaped articles from particulate mixtures areknown in the art. Classically, a desired particulate material is mixedwith a binder and then formed into the desired shape, this being calleda green body. The green body is then fired to fuse or sinter theparticulate material and to drive off the binder, thereby producing thedesired shaped product with proper surface texture, strength, etc.Modern methods include press and sinter (P&S) and powder injectionmolding (PIM). In P&S, a mixture of one or more of a metal, metal oxide,intermetallic or ceramic powder and a small amount of binder (about1-10%, or, on average, about 5% of the mixture by volume) are placed ina relatively simple mold, pressed into a green body, and then sintered.The small amount of binder is decomposed during the sintering step, so aseparate step of removing the binder is not necessary. However, P&S islimited to simple parts.

In PIM, a mixture of one or more of a metal, metal oxide, intermetallicor ceramic powder and a quantity of binder from 30% to 60% by volume ofthe mixture are heated to a liquid state and then injected underpressure into a mold to form a part. Once in the mold, the binder isremoved in one or more debinding steps and the part is fired to sinterthe particles into a solid part. PIM is capable of producing quitecomplex parts.

In the production of shaped objects by PIM in this manner, it has beenfound that the binder, while necessary to the process, create problems.The binder must be used in order to form an object of practical use, butmost of it must be removed before the part can be sintered, although insome cases a portion of the binder remains until sintering is completed.

Direct removal of the PIM binder during sintering is problematic. Manybinders leave behind ash upon decomposition. When such ash combines withcertain ingredients in the powder component, eutectic mixtures may beformed. Such eutectic compounds as TiC may be formed from titanium andcarbon ash, and these can result in serious problems in the formed part

Thermoplastic binders which decompose on heating have been used.However, previously known thermoplastic binders soften or melt first atlow temperatures but then do not decompose until much highertemperatures, i.e., above 400° C., thus creating problems ondecomposition. Thermoplastic materials have been tried which decomposeinto gaseous products below their melting point and thereby remain inplace until decomposition, but these require very careful heating inorder to avoid violent expansion of the gaseous products, which damagesparts. Binders also have been removed by exposure to a decomposingatmosphere, such as an acid atmosphere to decompose an acid-labileorganic binder. The drawback of this approach is the use of an acidatmosphere, requiring a special chamber and hazardous material handlingcapabilities. Binders which are subject to catalytic decomposition alsohave been used, such as a polyacetal. The drawback of this approach isthat the decomposition product is formaldehyde, which also requiresspecial equipment to collect and decompose the formaldehyde.

The prior art has recognized these problems and has therefore attemptedto remove the binder from the shaped green body prior to the step ofsintering. Such processes have used various solvents, including organicsolvents, supercritical fluid, such as triple-point CO₂, and water todissolve and remove the binder. While systems using such procedures canprovide advantages over procedures wherein the binder is removed duringfiring, articles formed by removing the binder prior to firing have atendency to crack during the binder removal as well as during the firingoperation. One reason for this is that the binder is removed from thegreen body by means of a solvent when the binder is in the solid state,and upon dissolution, the binder-solvent mixture has a tendency toexpand. This problem has been approached by various means, includingheating the green body prior to exposing it to the solvent, by using asolvent to remove a portion of the binder and removing the remainder byfiring, and by using a two-part binder, each part of which is soluble ina different solvent, so each solvent removes only a portion of thebinder, and using the different solvents in a stepwise manner. Each ofthese methods has its own drawbacks. All of these solvent-based methodssuffer from the necessity of dealing with the solvents and the problemsinherent therein, such as toxicity, recycling, evaporation losses andenvironmental considerations.

Thus, the need remains for binders which are useful, particularly inpowder injection molding, which require a minimum number of steps toremove, which have high thixotropic energy, which melt at lowtemperatures, which provide a green body having high strength, and whichdecompose thermally to yield simple, environmentally safe products,substantially free of ash. Such a binder would perform its functionwhile providing a process of powder injection molding which proceedswith a minimum number of process steps, can be carried out in an airatmosphere in many cases, and does not leave behind deleteriousresidues, either in the part or in the environment.

In addition to the foregoing needs, there exists a need for furthercontrol of the debinding process, by which the debinding time andtemperature can be adjusted and controlled over a wider range thanpreviously possible to match the characteristics of the inorganicmaterial of which the green composition is comprised.

SUMMARY OF THE INVENTION

The present invention uses only standard equipment which is commonlyavailable. The steps of both debinding and sintering of the inventivemethod may be carried out in the same equipment, on a continuous basis,thereby avoiding downtime for cooling and transfer from debindingequipment to sintering equipment.

In one embodiment, the present invention relates to a binder compositioncomprising an aliphatic polyester polymer; an ethylenebisamide wax; aguanidine wetting agent; and an additive which in use accelerates orextends debinding of the binder composition. The present inventionfurther relates to a method for forming a part by powder injectionmolding, including the steps of forming a green composition comprising abinder and an inorganic powder, wherein the binder is a compositioncomprising a polymer, an ethylenebisamide wax, a guanidine wetting agentand an additive; heating the green composition to debind the greencomposition, wherein the additive accelerates or extends the debindingstep. In one embodiment, the additive is a debinding accelerator whichincreases the rate of debinding of at least one of the first threeelements of the binder composition to accelerate the debinding step. Inone embodiment, the additive is a debinding extender which extends thetime and/or increases the upper temperature of, the debinding step. Inone embodiment the binder composition includes ingredients which debindby reverse debinding.

In another embodiment, the present invention relates to a bindercomposition comprising an aliphatic polyester polymer; anethylenebisamide wax; and a guanidine wetting agent. In one embodimentof the binder composition, the aliphatic polyester polymer is a polymerother than a poly(propylene) carbonate polymer. In one embodiment of thebinder composition, the aliphatic polyester polymer is a polymer otherthan a polycarbonate polymer. In one embodiment, binder compositioncomprises an aliphatic polyester polymer with the proviso that thealiphatic polyester polymer is not poly(propylene) carbonate polymer.

The present invention further relates to a method for forming a part bypowder injection molding, including the steps of forming a greencomposition comprising a binder and an inorganic powder, wherein thebinder is a composition comprising an aliphatic polyester polymer, anethylenebisamide wax, a guanidine wetting agent and heating the greencomposition to debind the green composition. In one embodiment of themethod, the composition includes an aliphatic polyester polymer which isa polymer other than a poly(propylene) carbonate polymer. In oneembodiment of the method, the binder composition further includes anadditive which in use accelerates or extends debinding of the bindercomposition. In one embodiment the debinding proceeds by reversedebinding.

In one embodiment of the method, the binder composition of the presentinvention may include both a debinding accelerator and a debindingextender. The debinding accelerator assists in quickly dispensing withthe lower-temperature-debinding components of the composition, while thedebinding extender extends the debinding and thereby assures that atleast some of the components of the debinding composition remain tomaintain the inorganic powder particles in place in the part until theonset of sintering.

Thus, the binder composition and method of making sintered parts usingthe binder composition of the present invention provide features missingfrom the prior art. The binder composition may be removed in a minimumnumber of steps, has high thixotropic energy, melts and becomes flowableat a low temperature, provides a green body having high strength, anddecomposes thermally to yield simple, environmentally safe products,substantially free of ash. In addition, when present, the additiveallows increased control of the timing and temperature of the debindingsteps as compared to a binder without the additive. The bindercomposition thereby performs its function while providing a process ofpowder injection molding which proceeds with a minimum number of steps,can be debound in air, hydrogen, oxygen, argon, nitrogen and similar gasatmospheres or in vacuum as appropriate. The binder composition does notleave behind deleterious residues, either in the part or in theenvironment. The binder composition debinds in a more controllablemanner, which can be adapted to correspond to the inorganic componentsto be bound and formed into the desired part. The debinding compositionprovides increased control of the debinding process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the steps in a method of making a partby powder injection molding in accordance with the present invention.

FIG. 2 is a graph of a debinding profile of an exemplary greencomposition which does not contain an additive.

FIG. 3 is a graph of a debinding profile of an exemplary greencomposition, similar to that of FIG. 2, but which contains a debindingaccelerator, according to the present invention.

FIG. 4 is a graph of a debinding profile of an exemplary greencomposition, similar to that of FIG. 2, but which contains a debindingextender, according to the present invention.

FIG. 5 is a graph of a debinding profile of an exemplary greencomposition, similar to that of FIG. 2, but which contains both adebinding accelerator and a debinding extender, according to the presentinvention.

DETAILED DESCRIPTION

The binder composition and the green composition comprising the bindercomposition and an inorganic powder, each in accordance with the presentinvention, are applicable both to powder injection molding (PIM)techniques and to press and sinter (P&S) applications. In PIM, a greencomposition or feedstock comprising an inorganic powder and a bindercomposition is used for powder injection molding, which includes stepsof debinding and sintering. In P&S applications, a green compositioncomprising an inorganic powder and a binder composition are pressed intoa mold and sintered to form a part, without a separate step ofdebinding. The green composition comprising an inorganic powder andbinder composition of the present invention, may be injection moldedwith an increased loading of the inorganic powder compared to priorprocesses, resulting in less shrinkage and deformation during debindingand sintering. The components of the binder composition allow debindingof the nascent part with decomposition of the binder to yieldenvironmentally safe products in a relatively rapid, controllableprocess, thereby efficiently overcoming the deficiencies of the priorart.

The inorganic powders which may be used in the compositions and methodsof the present invention may be metal, metal oxide, intermetallic and/orceramic, or mixtures of these, depending upon the desiredcharacteristics of the final product. The inorganic powder may be in theform of particles such as dusts, crystalline powders, amorphous powders,whiskers, short fibers, continuous fibers, microfibers, nanotubes, orany other form which may be used in PIM or P&S applications. The presentinvention is not limited to any particular form of the inorganic powder.

The components of the binder composition are partially miscible with oneanother, such that when the green composition is ready for use, thecomponents thereof are sufficiently miscible that the desired parts canbe formed when the composition is pumped into the mold, but thecomponents are sufficiently immiscible that the phases can separate andthe components will debind or ‘come apart’ in an orderly, controllablemanner in an oven or kiln during the debinding step. The bindercomposition of the present invention may be removed thermally, in thesame oven or chamber in which the part is sintered, thereby avoiding amultiple oven, multiple step process of debinding and sintering thepart.

The present inventors have discovered that, in addition to thecomponents of the binder composition controllably debinding in an orderwhich is the opposite of that normally sought in the PIM industry (i.e.,by reverse debinding), by judicious use of the presently disclosedadditives, the rate and/or temperature of the reverse debinding can befurther adjusted and controlled. During the debinding step of a PIMprocess which uses conventional binder compositions, e.g., stearic acidas a surface agent, paraffin wax as the wax, and polypropylene as themajor binder component, the surface agent releases first, the waxcomponent releases next, and the major binder component releases last.The rate of debinding in conventional binder compositions is difficultto control. Conventional binder compositions cannot provide a reversedebind, in which the polymeric component is the first component todebind.

The components of the binder composition of the present invention, incontrast, release in the opposite order, at temperatures below theboiling or vaporization temperature of the components, and providecontrol in the rate and/or temperature of debinding. This opposite orderof debinding is referred to as “reverse debinding.” In the bindercomposition of the present invention, the major binder component, analiphatic polyester polymer, has a decomposition temperature in therange from about 50° C. to about 250° C., when in the bindercomposition. The wax component, an ethylenebisamide wax, has adecomposition temperature of about 300-320° C., when in the bindercomposition. The guanidine wetting or surface agent has a decompositiontemperature in the range of about 270° C. to about 320° C., when in thebinder composition.

Thus, with the binder composition of the present invention, debindingcan be completed at a temperature as low as about 320° C., or less. Sucha low debinding temperature allows the processing of metals by PIM whichpreviously could not be processed by PIM due to the higher debindingtemperatures required by such conventional debinding compositions. Forexample, by using the binder composition of the present invention,metals such as aluminum, brass, beryllium and titanium can be formedinto parts by PIM. Such metals cannot be formed into parts by PIM usingconventional binder compositions.

In an embodiment including an additive which is a debinding accelerator,the time required at a given temperature, e.g., for the aliphaticpolyester polymer, to debind the first component can be selectivelyreduced. Alternatively, the temperature at which debinding begins can bereduced with a debinding accelerator. In an embodiment including anadditive which is a debinding extender, the time and/or temperaturerequired for completion of the debinding can be selectively increased.Thus, according to the present invention, when a debinding additive ispresent, during the debinding step of a PIM or P&S process, thecomponents of the binder composition debind in an order opposite to thatof conventional binder compositions, and the time and/or temperature ofdebinding can be controllably adjusted.

As a result of the reverse debinding profile of the binder compositionaccording to the present invention, the aliphatic polyester is the firstof the three primary binder ingredients (aliphatic polyester,ethylenebisamide wax and surface agent) to decompose in the debindingstep. When the additive is a debinding accelerator, the aliphaticpolyester is still the first to decompose and the surface agent and thebisamide wax still share the highest decomposition temperature. However,when the additive is a debinding extender, the debinding extenderdebinds after the surface agent and the bisamide wax, extending the timeand/or increasing the final temperature of debinding. As a result, whena debinding extender is the additive, the debinding extender serves toretain the inorganic powder in position for a longer time in thepre-sintering portion of the process. Retaining the inorganic powderparticles in position for a longer time provides the benefit of allowingthe transition from debinding to sintering to occur with a significantlyreduced possibility that the inorganic powder particles will move or bedistorted from their original position in the mold, and, in the case ofcertain high-temperature-sintering ceramics and high-temperature-meltingmetals, provides an extended time and/or temperature of binding, so thatthe particles are held in place by the binder for a longer time and to ahigher temperature, allowing them to begin to sinter in their intendedposition. As a result, superior sintered parts are obtained from the PIMprocess using the binder composition of the present invention.

While the inventors will not be bound by theory, it is believed thatdebinding of the aliphatic polyester takes place via loss of individualmolecules of aliphatic ester monomers from the free ends of thealiphatic polyester polymer chains. This process is referred to hereinas “end chain scission”. In end chain scission, individual monomermolecules are lost from the free ends of the polymer chains, and thegreater number of free ends, the faster the debinding.

It is believed that when the debinding accelerator is added to increasethe rate of debinding, the aliphatic polyester polymer chains are brokeninto shorter polymer chains by the debinding accelerator. As a result,the number of free ends is increased. The increase in the number of freeends increases the loss of monomers, thereby resulting in more rapiddebinding. The process of breaking the polymer chains into shorterpolymer chains is referred to herein as “main chain scission”. Thedebinding accelerator thus may be any molecule which cuts or scissionsthe main polymer chains into shorter polymer chains.

In one embodiment, the debinding accelerator is a free radical generatorapplied from an external source, such as ozone, gamma radiation orelectron beam, which appear to introduce free radicals which result inpolymer main chain scission.

In one embodiment, the accelerator is a metal or metal ions, such as atransition metal or ions, for example nickel, chromium or iron, andgenerally multivalent transition metals, which appear to catalyze bothend chain scission and main chain scission of the polymer.

When the ceramic or metal in the green composition to be formed into apart requires a temperature significantly higher than the debindingtemperature of the guanidine wetting agent, problems may result. This isdue to the fact that, at an interim time when all or substantially allof the binder has been debound from the green composition, and theinorganic component of the green composition has not yet begun tosinter, there is no binder to hold the particles of the inorganiccomponent together or in the relationship established in the greencomposition. The problem is that during the interim time, the particlesof the inorganic component may collapse or form voids, both of whichresult in a faulty part. The embodiment of the present invention inwhich the additive is a debinding extender is intended to address andsolve this problem.

The debinding extender is a molecule which has a higher decompositiontemperature than the highest-temperature debinding component of theoriginal three components, which is the guanidine wetting agent and/orthe ethylenebisamide wax. These components have a debind temperaturesuch that by the time the part reaches about 320° C., all orsubstantially all of the guanidine wetting agent and theethylenebisamide wax have been debound and removed. The debindingextender has a debind temperature generally in the range from about 450°C. to about 850° C. The desired debind temperature of the debindingextender can be selected in relation to the temperature at whichsintering begins in the high-temperature-sintering inorganic powdercomponent of the green composition, and selecting the debind extenderaccordingly. The debind temperature of the debinding extender willapproach or correspond to the temperature at which sintering of theinorganic powder begins. Thus, the part will remain bound untilsintering is initiated. Since the debinding extender debinds at a highertemperature, debinding a green composition containing the debindingextender as the additive will extend debinding for a longer time and/orto a higher temperature.

The partial miscibility of the components of the binder compositionfacilitates the reverse debinding of the present invention. Since thealiphatic polyester polymer is only partially miscible with the othercomponents and has a lower glass transition (T_(g)) and meltingtemperature, it can decompose by end chain scission to formdecomposition products, e.g., the monomer, which can separate from theother components of the binder composition, and wick out of the greenpart first.

As generally described above, the binder composition of the presentinvention comprises an aliphatic polyester polymer, a wax such asethylenebisamide wax, and a guanidine wetting agent, and, in someembodiments, a debind rate control additive. Each of these three generalcomponent materials and each of the additives are more fully disclosedin the following.

In the specification and claims the range and ratio limits may becombined.

Guanidine Wetting Agent

In one embodiment, the guanidine wetting agent is a reaction product ofguanidine and an acid selected from a fatty acid, an organic acid, and astronger acid such as an alkyl sulfonic acid.

The particular acid used to make the reaction product of guanidine andan acid may be selected based on various factors including the surfacecharge of the inorganic powder with which the binder composition is tobe used. In one embodiment, the guanidine wetting agent is guanidinestearate. In one embodiment, the guanidine wetting agent is guanidine2-ethylhexanoate. In other embodiments, the guanidine wetting agent maybe the reaction product of guanidine and other acids. The selection ofthe appropriate acid for preparation of the reaction product ofguanidine and an acid can be facilitated by the measurement of theisoelectric point of the inorganic powder, and is further described inU.S. Pat. Nos. 6,093,761 and 6,204,316, the disclosures of which arehereby incorporated by reference for their teachings relating toguanidine wetting agents.

In one embodiment, the guanidine wetting agent comprises a mixture oftwo or more guanidine wetting agents. In particular, the presentinventors have discovered that blends of guanidine stearate andguanidine 2-ethylhexanoate provide excellent results for inorganicpowders having isoelectric points equal to or less than about 8.

In one embodiment, the mixture of guanidine wetting agents includesabout 45 wt % of guanidine stearate and about 55 wt % guanidine2-ethylhexanoate, and in another, the mixture includes about 75 wt %guanidine stearate and about 25 wt % guanidine 2-ethylhexanoate. Inanother embodiment, the mixture comprises from about 35 wt % to about 80wt % guanidine stearate and from about 65 wt % to about 20 wt %guanidine 2-ethylhexanoate. The ratio of these two guanidine compoundsmay be varied as needed to provide the desired rheologicalcharacteristics for the binder composition and for the green compositionof interest in a particular application.

The mixture of guanidine wetting agents may be varied to as to obtain amaximum loading of inorganic powder in the green composition, whileretaining the desired rheology characteristics. Thus, for example,increasing the ratio of guanidine stearate to guanidine 2-ethylhexanoatemay allow use of a higher loading of inorganic powder, while allowingthe green composition to retain its desirable rheology characteristics.As a result, a superior part is obtained, i.e., one with reducedsintered shrinkage and porosity, while retaining the ability to easilyinjection mold the green composition.

While a certain amount of trial and error may be required to optimizethe reaction product of guanidine and an acid for a particular inorganicpowder, and particularly for a combination of inorganic powders, theselection can be guided by the foregoing disclosure. The acid selectedshould be rheologically compatible with the compounding and injectionmolding equipment. Some testing may be required in order to optimize theacid or mixture of acids for reaction with guanidine to form theguanidine wetting agent for a given inorganic powder, or to determinethe optimum ratio of two guanidine wetting agents such as describedabove.

Aliphatic Polyester Polymer

In one embodiment, the binder composition of the present inventionincludes an aliphatic polyester polymer having a number averagemolecular weight (M_(n)) in the range from about 60,000 to about120,000. In another embodiment, the aliphatic polyester polymer M_(n) isin the range from about 70,000 to about 90,000. In another embodiment,the aliphatic polyester polymer M_(n) is about 80,000.

The aliphatic polyester provides at least three functions in the bindercomposition of the present invention. First, the aliphatic polyesterserves as a non-Newtonian fluid carrier for the inorganic powdercomponents, which assists in molding the green composition into adesired form in preparation for fusion of the inorganic powdercomponents. Second, the aliphatic polyester contributes strength inmaintaining the molded shape of the green composition prior to thefusion. Third, the aliphatic polyester is completely removable from thegreen composition at a selected time in a controlled manner, withouteither forming gaseous products or leaving behind a residue such as ash.Only a limited number of aliphatic polyesters meet all three of thesecriteria.

The general class of aliphatic polyesters may be divided into threegroups, designated as aliphatic polyester groups A, B and C. Aliphaticpolyester group A includes the polymeric reaction products of aliphaticdicarboxylic acids and aliphatic diols. Aliphatic polyester group Bincludes the polymeric reaction products of hydroxy acids. Aliphaticpolyester group C includes the polycarbonates, the polymeric reactionproducts of carbon dioxide and cyclic ethers, such as epoxides. Each ofthese groups is more fully described in the following.

Aliphatic Polyester Group A

The aliphatic polyester polymers in group A include the followinggeneral formula (A): wherein R and R′ are independently a single bond ora C₁-C₁₀ saturated or unsaturated aliphatic, straight chain, branchedchain, cyclic or alicyclic group, which group may include one or more of—O—,

—S—, —S—S—, —SO₂—, or —C(O)—; and n=about 50 to about 500, and whereinmixtures of R and R′ may be included, to form copolyesters.

The aliphatic polyesters in group A are generally prepared by thereaction of the appropriate dicarboxylic acid or a derivative thereofsuch as an acid chloride, an anhydride or an ester, with suitabledihydroxy compounds such as diols or epoxides. However, other methods ofproducing aliphatic polyesters are known and the resulting polyesterswhich meet the functional requirements of this invention are includedwithin the scope of the present invention. For example, polyesterpolymers may be made by reacting methyl esters of dicarboxylic acidswith a suitable diol in a transesterification reaction.

Small amounts of carboxylic acid or hydroxy functional aliphaticmaterials containing more than 2 functional groups may also beincorporated in the aliphatic polyesters of group A. Thesemultifunctional materials result in crosslinking of the polymer chains.However, such multi-functional groups should be limited to less thanabout 5 wt % of the aliphatic polyester to prevent the formation of agel or excessively crosslinked polymeric material. In one embodiment,the amount of multi-functional components is less than 2 wt % of thealiphatic polyester.

In one embodiment, the aliphatic polyester of group A is polyethyleneadipate.

Examples of the polymers in the aliphatic polyester polymer group Ainclude: poly (hexamethylene oxalate); poly (ethylene suberate); poly(ethylene sebacate); poly (decamethylene oxalate); poly (hexamethylenesuberate); poly (decamethylene succinate); poly (decamethylene adipate);poly (hexamethylene sebacate); poly (ethylene succinate); poly(eicosamethylene diglycolate); poly (eicosamethylene thiodivalerate);poly (eicosamethylene sulfonyl divalerate); poly (tetramethylened-2-β-dimethoxy succinate); poly (meso-tetramethylene d-2β-dimethoxysuccinate); poly (hexamethylene fumarate); poly (hexamethylenesuccinate); poly (trans-2-butenylene sebacate); poly (tetramethylenesebacate); poly (cis-2-butenylene sebacate);poly(trans-1,4-cyclohexylene dimethylene adipate); poly(cis-1,4-cyclohexylene dimethylene adipate); poly(cis-1,4-cyclohexylenedimethylene succinate): poly(trans-1,4-cyclohexylenedimethylene succinate); poly (decamethyleneazelaate); poly (decamethylene glutarate); poly (decamethylene3-hexenedioate); poly (decamethylene octadecanedioate); poly(decamethylene sebacate); poly (decamethylene suberate); poly(dodecamethylene adipate); poly (dodecamethylene 3-hexenedioate); poly(dodecamethylene suberate); poly (hexadecamethylene adipate); poly(hexadecamethylene 3-hexenedioate); poly (trans-hexadecamethylene4-octenedioate); poly (hexadecamethylene suberate); poly (hexamethyleneadipate); poly (hexamethylene 3-hexenedioate); poly (nonamethyleneazelaate); poly (octamethylene adipate); poly (octamethylene3-hexenedioate); poly (octamethylene suberate); poly (tetradecamethyleneadipate); poly (tetradecamethylene 3-hexenedioate); poly(tetradecamethylene 4-octenedioate); poly (tetradecamethylene suberate);poly (tetramethylene sebacate); poly (tetramethylene succinate); poly(trimethylene azelaate); poly (trimethylene adipate); poly (trimethylenedodecanedioate); poly (trimethylene octadecanedioate); poly(trimethylene sebacate); poly (trimethylene undecanedioate); poly(trimethylene suberate); poly (decamethylene octadecanedioate); poly(decamethylene oxalate); poly (decamethylene sebacate); poly (ethyleneadipate); poly (ethylene azelaate); poly (ethylene suberate); poly(ethylene succinate); poly (nonamethylene azelaate); poly (trimethylenesuccinate); poly (decamethylene adipate), mixtures thereof and similaraliphatic polyesters falling within the definition provided above forthe aliphatic polyesters of aliphatic polyester group A.

Aliphatic Polyester Group B

The aliphatic polyester polymers in group B include the followinggeneral formula (B):

wherein R″ is a C₂-C₁₈ saturated or unsaturated aliphatic, straightchain, branched chain, cyclic or alicyclic group, which group mayinclude one or more of —O—, —S—, —S—S—, —SO₂—, or —C(O)—; and m=about200 to about 2000. The polyesters in group B are generally preparedeither by a self-condensation reaction between one or more hydroxy acidsor their lower alkyl esters or by the ring opening polymerization of thecyclic derivatives of one or more hydroxy acids. The cyclic derivativesare known as lactones, lactides or more generally as the cyclicmonomers, dimers, trimers or tetramers, etc of the corresponding hydroxyacids.

In one embodiment, the group B aliphatic polyester polymer ispolycaprolactone. In one embodiment, the polycaprolactone is ahomopolymer of ε-caprolactone, a seven-membered ring compound. Thehomopolymer of ε-caprolactone may be represented by the followingstructure:

During the debinding process, polycaprolactone decomposes cleanly toform ε-caprolactone, a seven-membered ring compound mentioned above asthe monomer for ε-caprolactone. Thus, polycaprolactone may be consideredto simply depolymerize in the debinding process. ε-caprolactone has thefollowing structure:

The ε-caprolactone has a boiling point of 235° C.

In one embodiment, the polycaprolactone polymer is a polycaprolactoneproduced by Union Carbide Corporation, Danbury, Conn., and marketedunder the tradename of TONE®. Two polycaprolactone polymers are marketedunder the tradename of TONE®, P-767 and P-787. Both of these polymersare homopolymers of ε-caprolactone, and may be represented by thefollowing structure:

in which R is diethylene glycol and the total of p and q may range fromabout 400 to about 800. The approximate Mn molecular weights of theTONES P-767 and P-787 are in the range from about 50,000 to about90,000.

In other embodiments, the group B aliphatic polyester polymer may be oneof the following specific examples: poly (3-hydroxy-3-butenoic acid);poly (10-hydroxycapric acid); poly (6-hydroxycaproic acid); polycis-(5-hydroxymethyl-2-(1,3-dioxolane)-caprylic acid; poly(3-hydroxyproplonic acid); poly (3-ethyl-[hydroxy valeric acid]); poly(2-ethyl-2-methyl-[3-hydroxyvaleric acid]); poly (3-isopropyl-[3-hydroxyvaleric acid]); poly (2-methyl-[3-hydroxyvaleric acid]); poly(d,1-2-methyl-2-propyl-[3-hydroxyvaleric acid]), mixtures thereof andsimilar aliphatic polyesters falling within the definition providedabove for the aliphatic polyesters of aliphatic polyester group B.

Aliphatic Polyester Group C

The aliphatic polyester polymers in group C include the followinggeneral formula (C):

wherein R⁴ and R⁵ are independently a single bond or a C₁-C₁₀ saturatedor unsaturated aliphatic, straight chain, branched chain, cyclic oralicyclic group, which group may include one or more of —O—, —S—, —S—S—,—SO₂—, or —C(O)— as a substituent, provided that at least one of R⁴ andR⁵ are other than a single bond; and X and Y are selected such that thetotal of X and Y yields a polymer having a Mn molecular weight in therange from about 30,000 to about 180,000, wherein mixtures of R⁴ and R⁵may be included, to form copolyesters. The foregoing aliphaticpolyesters in group C are also known as polycarbonate aliphaticpolyesters.

In one embodiment, the aliphatic polyesters of group C are polycarbonatealiphatic polyesters such as: poly (ethylene carbonate); poly(1,2-propylene carbonate); poly (1,3-propylene carbonate); poly(1,2-butylene carbonate); poly (1,3-butylene carbonate); poly(1,4-butylene carbonate); poly (1,2-pentylene carbonate); poly[1,3-(2,2-dimethyl propylene carbonate)]; poly (1,5 pentylenecarbonate); and poly (1,6-hexylene carbonate), mixtures thereof andsimilar aliphatic polyesters falling within the definition providedabove for the aliphatic polyesters of aliphatic polyester group C.

In one embodiment, the group C polycarbonate aliphatic polyester ispoly(propylene carbonate). Poly(propylene carbonate) may be preparedfrom the reaction of carbon dioxide, CO₂, and propylene oxide,CH₂═CH(O)CH₂, as shown in the following:

The poly (propylene carbonate) shown above, on application of sufficientheat, decomposes into a compound having the following structure, whichis a liquid having a boiling point near the decomposition temperature ofthe poly (propylene carbonate):

In one embodiment, the polycarbonate polymer has a Mn molecular weightin the range from about 25,000 to about 75,000. In one embodiment, thepolycarbonate polymer has a Mn molecular weight in the range from about35,000 to about 65,000. In one embodiment, the polycarbonate polymer hasa Mn molecular weight in the range from about 35,000 to about 40,000. Inone embodiment, the polycarbonate polymer has a Mn molecular weight ofabout 50,000. In one embodiment the polycarbonate polymer has a Mnmolecular weight in the range from about 45,000 to about 55,000.

In one embodiment, the polycarbonate polymer is Q-PAC™ 40, availablefrom PAC Polymers, a division of Axcess Corporation, Newark, Del. Q-PAC™40 is a low molecular weight polycarbonate, having a Mn molecular weightin the range of about 50,000. Q-PAC™ 40 has a glass transitiontemperature, T_(g)=40° C. The cyclic monomer shown above is a lowboiling liquid, having a boiling point of 242° C. Thus, at relativelymoderate temperatures, Q-PAC™ 40 decomposes to form a low melting liquidwhich exits the green form as a liquid having only a slightly increasedvolume with respect to the solid, rather than decomposing into a gashaving a greatly increased volume with respect to the solid. As above,the partial miscibility of the polycarbonate polymer allows it to meltand separate from the remaining components of the green compositionduring the debinding process.

Other embodiments of the aliphatic polyester polymers debind bydecomposing in a similar manner, to yield low-melting liquid, as opposedto gaseous, decomposition products. The liquid decomposition productsthen exit the green composition smoothly with little change in volume.

The decomposition products of poly(propylene carbonate) andpolycaprolactone shown above are exemplary of such decompositionproducts from the presently disclosed aliphatic polyester polymers, ofall three types. The decomposition products have melting points belowthe temperature at which the polymer decomposes. Thus, as the bindercomposition of the present invention is heated following being mixedwith the inorganic powder to form the green composition and injectedinto a mold, the aliphatic polyester polymer first melts and then beginsto decompose into the liquid cyclic propylene carbonate shown above. Onfurther heating in the debinding process, the cyclic monomer decomposescleanly in air to form CO₂ and water. Thus, according to the presentinvention, the aliphatic polyester polymer is the first component to belost from the green composition in the debinding process. In contrast,in the prior art binders, the polymeric component has been designed tobe and was the last component lost from the binder during the debindingprocess.

While not being bound by theory, it is believed that the aliphaticpolyester polymer is debound by first melting and then undergoing endchain scission to form a liquid monomer, which may exit as a liquid andmay then be decomposed to gaseous or vaporized decomposition products.

Ethylenebisamide Wax

The binder composition of the present invention includes anethylenebisamide wax. The ethylenebisamide wax is a wax formed by theamidization reaction of ethylene diamine and a fatty acid. The fattyacid of the bisamide wax may be any fatty acid in the range from aboutC₈ to about C₃₀, or from about C₁₂ to about C₂₂, and may be saturated orunsaturated. In one embodiment, the fatty acid is stearic acid, asaturated C₁₈ fatty acid. Thus, in one embodiment, the ethylenebisamidewax is ethylenebisstearamide wax. In one embodiment theethylenebisstearamide is ACRAWAX® C, available from LONZA, Inc.

In other embodiments of the binder composition, other ethylenebisamidesinclude the bisamides formed from fatty acids such as octanoic acid,2-ethyl-hexanoic acid, decanoic acid, lauric acid, palmitic acid, oleicacid, linoleic acid, linolenic acid, oleostearic acid, stearic acid,myristic acid, undecylenic acid, behenic acid (docosanoic acid),tetracosanoic acid, hexacosanoic acid, and octacosanoic acid.Unsaturated fatty acids may be used as well as saturated fatty acids.

Additives

Debinding Accelerators

In one embodiment, the binder composition comprises an aliphaticpolyester polymer; an ethylenebisamide wax; a guanidine wetting agent;and an additive which in use accelerates debinding of the bindercomposition. In one embodiment, the debinding accelerator is a generatorof free radicals, such as a peroxide or an azo compound. Although not tobe bound by theory, it appears the free radical generated by the freeradical generator attacks the aliphatic polyester polymer chain,scissioning the chain in the process referred to herein as chainscission. In one embodiment, the accelerator is a metal, such as atransition metal, for example, one or more of nickel, chromium and iron.In the metal embodiment, although not to be bound by theory, it appearsthat the metal catalyzes both main chain scission, i.e., breaking thelong polymer chain into chains of reduced length, and end chainscission, i.e., loss of monomeric units from the ends of the polymerchains. Furthermore, again not to be bound by theory, it appears that itis the ionic form of the metals, i.e., metals in the form of compoundssuch as oxides, carboxylates or other salts, which catalyze the scissionreactions.

Organic Peroxide Debinding Accelerators

In one embodiment, the debinding accelerator is an organic peroxide. Inone embodiment, the debinding accelerator is an azo compound.

In one embodiment, the debinding accelerator is a dialkyl peroxide. Thedebinding accelerator may be a symmetrical dialkyl peroxide or anon-symmetrical dialkyl peroxide. In one embodiment, the alkyl group ofthe dialkyl peroxide is substituted with one or more of a halogen, anitro-group, a hydroxyl group, an amine group, an amide group, acarbonyl group, a carboxyl group, or an anhydride group. In oneembodiment, the debinding accelerator is an organic hydroperoxide. Inone embodiment, the debinding accelerator is a diaryl peroxide. In oneembodiment, the debinding accelerator is a symmetrical diaryl peroxide.In one embodiment, the debinding accelerator is a non-symmetrical diarylperoxide. In one embodiment, the aryl group is substituted with one ormore of a halogen, a nitro-group, a hydroxyl group, an amine group, anamide group, a carbonyl group, a carboxyl group, or an anhydride group.In one embodiment, the organic peroxide is an arylalkyl peroxide, i.e.,a peroxide such as t-butyl benzyl peroxide. In such an embodiment,either or both of the alkyl group or the aryl group may be substitutedas disclosed above for dialkyl and diaryl peroxides.

Suitable organic peroxides for the debinding accelerator embodiment ofthe additive of the present invention include at least one of thefollowing: dicumyl peroxide, di-t-butylperoxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-amylperoxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,α,α′-di(t-butylpemxy)diisopropylbenzene, decanoyl peroxide, lauroylperoxide, succinic peroxide, 2-dihydroperoxybutane and multimersthereof, 2,4-pentanedione peroxide, di(n-propyl)peroxydicarbonate,di(sec-butyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate,1,1-dimethyl-3-hydroxybutyl peroxyneodecanoate, α-cumylperoxyneodecanoate, 1,1-dimethyl-3-hydroxybutyl penoxyneoheptanoate,α-cumyl peroxyneoheptanoate, t-amyl peroxyneodecanoate, t-butylperoxyneodecanoate, t-amyl pemoxypivalate, t-butyl peroxypivalate,2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy) hexane,t-amylperoxy-2-ethylhexanoate, t-butyl peroxyacetate, t-amylperoxyacetate, t-butyl perbenzoate, t-amyl perbenzoate,O,O-t-amyl-O-(2-ethylhexyl)monoperoxycarbonate,di-t-butyldiperoxyphthalate, t-butylcumylperoxide,O,O-t-butyl-O-(isopropyl)monoperoxycarbonate,2,5-dimethyl-2,5-di(benzoylperoxy) hexane,O,O-t-butyl-1-(2-ethylhexyl)monoperoxycarbonate, cumene hydroperoxide,t-butyl hydmoperoxide, t-amyl hydroperoxide,1,1-di(t-butylperoxy)-3,3,5-trimethyl-cyclohexane,1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-amylperoxy)cyclohexane,ethyl-3,3-di(t-butylperoxy)butyrate, andethyl-3,3-di(t-amylperoxy)butyrate,1,3-bis(t-butylperoxyisopropyl)benzene, 1,1-bis(t-butylperoxy)valerate,benzoyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoylperoxide, 3,5,5-trimethylhexanoyl peroxide, 2,4-dichlorobenzoylperoxide, m-toluyl peroxide, methylethylketone peroxide, cyclohexanoneperoxide, 3,5,5-trimethylhexanone peroxide, 1,1-bis (t-butylperoxy)-3,3,5-trimethylhexane, 1,1-bis (tbutyl peroxy)-cyclohexane,2,2-bis (t-butyl peroxy) octane, diisopropylbenzene hydroperoxide,diisopropyl peroxydicarbonate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy neodecanate, t-butyl peroxy laurate, t-butyl peroxyisopropylcarbonate, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane,2,2′-bis(t-butylperoxy)-diisopropylbenzene,4,4,′-bis(t-butylperoxy)butylvalerate, t-butylperterephthalate,2,2-di-(t-butylperoxy)butane, n-butyl 4,4′-di-tbutylperoxyvalerate,2,4-dichlorobenzoyl peroxide, o-chlorobenzoyl peroxide,t-butylperoxyneohexanoate, di-(3-methoxybutyl)peroxydicarbonate,4,4′-dichloro benzoyl peroxide, tert-butylperoxymaleic acid,2,4-pentanedione peroxide and 2,5-dimethyl2,5-di(2-ethylhexanoylperoxy)hexane. Other aromatic peroxides may be used, such as anthraceneperoxide and naphthalene peroxide. The foregoing list is intended to beexemplary, and suitable peroxides not included here may be selected bythose of skill in the art based on similarities to the foregoing list.In particular, for example, it is noted that any of the foregoingperoxides may be substituted by any of the substituents identifiedabove.

In one preferred embodiment, the organic peroxide is2,5-dimethyl-2,5-di(t-butylperoxy)hexane. In one embodiment, the organicperoxide is benzoyl peroxide. In one embodiment, the organic peroxide isperoxy benzoic acid.

In general, the organic peroxides may be described by the generalformulas R₁₀O-O-R₁₁ or R₁₀-O-O-R₁₁-O-O-R₁₂ wherein R₁₀, R₁₁, and R₁₂ areeach independently alkyl, aryl, substituted alkyl or substituted aryl.

Particularly preferred organic peroxides are dialkyl peroxides where theterm alkyl radical is defined as a conventional saturated straight-chainor branched lower alkyl radical having up to six carbon atoms.

Many of the foregoing peroxides are liquids at room temperature, or havea relatively low melting point. In such cases, it has been foundadvisable and helpful to place, or adsorb, the peroxides on a solidcarrier. Such solid carriers may be one or more of a polyolefin, a clay,calcium carbonate or silica, or similar known carrier materials. Whenthey are absorbed on such carriers, the weight percentage of organicperoxide ranges specified above do not include the particulate carrier.In one embodiment, the solid carrier is a relatively low molecularweight polymer such as polypropylene or polyethylene. Since theperoxides are intended to assist in and accelerate debinding of thealiphatic polyester polymer component of the binder composition, themolecular weight preferably is such that the solid carrier decomposes ata temperature somewhat above 180° C., the temperature of debinding ofthe aliphatic polyester component. An organic, ash-free solid carrier ispreferred, since such a carrier will decompose to produce the sameinnocuous, gaseous products (CO₂ and H₂O) as produced by the aliphaticpolyester.

In one embodiment, the solid carrier material upon which the debindingaccelerator is adsorbed is an inorganic material such as calciumcarbonate or silica. In such embodiments, while it may appearundesirable to include materials such as calcium or silicon which willnot debind into gaseous or liquid products, the amounts of carrier arerelatively small, and in most cases do not appreciably affect thequality of the parts so produced. In cases where even a trace of suchmaterials is undesirable or prohibited, other, higher-melting organicperoxides may be suitably selected.

Inorganic Peroxide Debinding Accelerators

In one embodiment, the free radical source may be an inorganic peroxide.In one embodiment, the inorganic peroxide is one which decomposes toyield products which do not produce ash. In one embodiment, theinorganic peroxide is ammonium peroxysulfate ((NH₄)₂S₂O₈). In oneembodiment, the inorganic peroxide is a volatile peroxysulfate. Avolatile peroxysulfate is one which decomposes to yield ash-free orlow-ash products. In one embodiment, the inorganic peroxide is avolatile peroxynitrate. A volatile peroxynitrate is one which decomposesto yield ash-free or low-ash products. In one embodiment, the inorganicperoxide is urea peroxide. In one embodiment, the inorganic peroxide ishydrogen peroxide.

Azo Compound Debinding Accelerators

In another embodiment, the free radical source utilized as the debindingaccelerator may be an azo compound. Suitable azo compounds include, forexample: 2,2′-azobisisobutyronitrile,2,2′-azobis-2,4-dimethylvaleronitrile, 4,4-azobis-4-cyano valeric acid,1-azobis-1-cyclohexane carbonitrile, dimethylazoisobutyronitrile anddimethyl2,2′-azobis-isobutylate. Other similar, known azo compounds maybe suitably selected. Further examples include:2,2′-azobis(2-methylbutanenitrile) and1,1′-azobis(cyclohexanecarbonitrile).

Metal Debinding Accelerators

In one embodiment, the debinding accelerator is a metal. In oneembodiment, the metal is a transition metal, for example one or moremetal selected from the metals in Groups IIIb, IVb, Vb, VIb, VIIb, VIII,Ib and IIb of the Periodic Table of the Elements. For example, the metalmay be one or more of titanium, chromium, manganese, Iron, nickel,copper or zinc. In one embodiment a small amount of the metal debindingaccelerator is added to the binder composition for use with an inorganicpowder which is to be formed into a solid part by PIM or P&S.

Other Debinding Accelerators

In addition, in other embodiments the debinding accelerator may be anysource of free radicals which can scission the aliphatic polyesterpolymer chain. Thus, for example, treating the green composition withozone or radiation such as gamma rays, electron sources such as electronguns, electric arc and plasmas may be useful for accelerating debinding.The debinding accelerator need only provide a free electron which canscission the polymer chain into smaller polymers, as described above.

Debinding Extender

In one embodiment, the present invention relates to a binder compositioncomprising: an aliphatic polyester polymer; an ethylenebisamide wax; aguanidine wetting agent; and an additive which extends debinding of thebinder composition. In one embodiment, the additive is a debindingextender which extends debinding to higher temperatures and/or longerdebind times.

In one embodiment, the debinding extender is a polymer having adebinding temperature in the range from about 450° C. to about 850° C.,or from about 500° C. to about 750° C., or from about 475° C. to about700° C., or from about 450° C. to about 750° C. In one embodiment, thedebinding extender is a polymer having a debind temperature greater thanthe debind temperature of the guanidine wetting agent andethylenebisamide wax with which the debinding extender is combined inthe debinding composition.

While the debinding extender may be any polymer which has a suitabledebinding temperature and which debinds by decomposing into simple, safemolecules, certain debinding extenders are preferred. In one embodiment,the debinding extender is at least one of a polypropylene polymer or apolymethacrylate polymer. The debinding extender may be a suitableacrylate polymer. In one embodiment, the debinding extender is anatactic polypropylene, or a syntactic polypropylene, or an isotacticpolypropylene, or a mixture of any two or all three of atactic,syntactic and isotactic polypropylene. In one embodiment, when theinorganic powder is a ceramic material, silicone resins may be used asthe debinding extender. For example, the WACKER M series resins areuseful in this regard.

In one embodiment, the debinding extender is a polypropylene copolymeravailable under the trade name ProFlow 3000 from Polyvisions, Inc.,York, Pa.

In one embodiment, the debinding extender is a polymethacrylate polymer.In another embodiment, the debinding extender is apoly-alkylmethacrylate polymer. The alkyl substituent may be a C₁-C₁₀alkyl group. In one embodiment, the debinding extender is apolymethylmethacrylate polymer (PMMA).

In one embodiment, the debinding extender is a polymer having a weightaverage molecular weight in the range from about 25,000 to about250,000, or from about 40,000 to about 120,000. In one embodiment, thedebinding extender is a polypropylene polymer which has a weight averagemolecular weight of about 50,000. In one embodiment, the debindingextender is a polymethacrylate polymer which has a weight averagemolecular weight of about 100,000.

In another embodiment, the debinding extender is a polyethylene polymer,or a polyacrylate polymer, or a copolymer of ethylene and propylene.Additional polymers which may be suitable as the debinding extenderinclude polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral,polypropenal, polyacetal and polystyrene, or a copolymer of theforegoing polymers, for example, an acrylateipropylene copolymer.

Quantities of Components in the Binder and Green Compositions

It is a practice in the art of powder metal to refer to a bindercomposition in terms of parts by weight, or percent of each component ona weight basis, and to refer to a green composition in terms of parts byvolume, or percent of each component on a volume bases. Thus, the amountof each component in the binder composition is expressed as weightpercent, or wt %. The amounts of the inorganic powder and the bindercomposition combined to form the green composition are expressed asvolume percent, or vol %. This practice is followed throughout thepresent specification and claims.

In one embodiment, the binder composition comprises the guanidinewetting agent in the range from about 5 wt % to about 30 wt % based onthe binder composition, the aliphatic polyester polymer in the rangefrom about 30 wt % to about 85 wt % based on the binder composition, andthe ethylenebisamide wax in the range from about 10 wt % to about 40 wt% based on the binder composition. Additional information relating tothe quantities of the components of the binder composition can be foundin the examples.

In one embodiment, the binder composition comprises the guanidinewetting agent in the range from about 0.1 wt % to about 50 wt % based onthe binder composition, the aliphatic polyester polymer in the rangefrom about 20 wt % to about 75 wt % based on the binder composition, andthe ethylenebisamide wax in the range from about 20 wt % to about 40 wt% based on the binder composition. In one embodiment of the bindercomposition, the guanidine wetting agent is present at about 15 wt %,the aliphatic polyester polymer is present at about 59 wt %, andethylenebisstearamide is present at about 25 wt %, each weight percentbased on the binder composition.

In one embodiment, the aliphatic polyester polymer is a polycaprolactonepolymer, which in one embodiment is TONE® P-787 brand ofpolycaprolactone, and is present at about 59 wt % of the bindercomposition. In one embodiment, the aliphatic polyester polymer is TONE®P-787 brand of polycaprolactone, and is present at about 25 wt % of thebinder composition.

In one embodiment, the ethylenebisamide is ACRAWAX® C brand ofethylenebisstearamide, and is present at about 22 wt % of the bindercomposition. In one embodiment, the ethylenebisamide is ACRAWAX® C brandof ethylenebisstearamide, and is present at about 31 wt % of the bindercomposition.

In one embodiment, the guanidine wetting or surface agent is present atabout 15 wt % to about 45 wt %, based on the binder composition. In oneembodiment, the guanidine wetting agent is a mixture of two or moreguanidine compounds. In one embodiment, the guanidine agent is a mixtureof guanidine stearate and guanidine 2-ethylhexanoate. In one embodiment,when these two agents are present together, the ratio between theguanidine stearate and guanidine 2-ethylhexanoate varies from about 1:5to about 5:1. In one embodiment, the ratio is about 1:1, in one about1:3, in one about 3:1, respectively.

In one embodiment, the binder composition comprises the guanidinewetting agent in an amount from about 10 wt % to about 50 wt %, thealiphatic polyester polymer in an amount from about 20 wt % to about 75wt %, and the ethylenebisamide wax in an amount from about 15 wt % toabout 40 wt %, each based on the binder composition. In anotherembodiment, the binder composition comprises the guanidine wetting agentin an amount from about 10 wt % to about 25 wt % based on the bindercomposition, the aliphatic polyester polymer in an amount from about 40wt % to about 60 wt % based on the binder composition, and theethylenebisamide wax in an amount from about 15 wt % to about 35 wt %based on the binder composition.

When an additive which is a debinding accelerator or a debindingextender is added, the relative amounts of the aliphatic polyester, theethylenebisamide wax and the guanidine wetting agent generally remainthe same, but the addition of the additive reduces the proportion ofeach of these components of the total binder composition, in proportionto the quantity of additive which is added.

In one embodiment, when the additive is a debinding accelerator, thedebinding accelerator is present in the range from about 0.01 wt % toabout 3 wt % of the binder composition, or from about 0.05 wt % to about1 wt % of the binder composition, or from about 0.25 wt % to about 0.5wt % of the binder composition, or from about 0.01 wt % to about 0.03 wt% of the binder composition, or from about 0.35 wt % to about 0.45 wt %.

In one embodiment, when the additive is a debinding extender, thedebinding extender is present in the range from about 1 wt % to about 20wt % of the binder composition, or from about 6 wt % to about 8 wt % ofthe binder composition, or from about 14 wt % to about 16 wt % of thebinder composition, or from about 7 wt % to about 13 wt % of the bindercomposition. The binder composition of the present invention may also beused for P&S applications. In such applications, the binder compositioncomprises the guanidine wetting agent in the range from about 5 wt % toabout 30 wt % based on the binder composition, the aliphatic polyesterpolymer in the range from about 10 wt % to about 50 wt % based on thebinder composition, and the ethylenebisamide wax in the range from about30 wt % to about 70 wt % based on the binder composition.

In one embodiment, when the additive is a debinding accelerator in a P&Sapplication, the debinding accelerator is present in the range fromabout 0.01 wt % to about 3 wt % of the binder composition, or from about0.25 wt % to about 0.5 wt % of the binder composition, or from about 0.1wt % to about 0.25 wt % of the binder composition.

In one embodiment, when the additive is a debinding extender in a P&Sapplication, the debinding extender is present in the range from about 1wt % to about 20 wt % of the binder composition, or from about 7 wt % toabout 9 wt % of the binder composition, or from about 15 wt % to about18 wt % of the binder composition.

The binder composition of the present invention is designed to becombined with an inorganic powder, to form a green composition for usein PIM or P&S. For PIM, in one embodiment the green composition includesthe binder composition, as described above, and at least one inorganicpowder selected from a metal powder, a metal oxide powder, anon-metallic powder and a ceramic powder. In one embodiment, the greencomposition includes the binder composition in an amount in the rangefrom about 30 vol % to about 60 vol % and the inorganic powder orpowders in an amount from about 70 vol % to about 40 vol %, or thebinder composition from about 40 vol % to about 50 vol % and theinorganic powder from about 60 vol % to about 50 vol %, or the bindercomposition at about 35 vol % and the inorganic powder at about 65 vol%.

The binder composition of the present invention is also suitable for usewith an inorganic powder, to form a green composition for use in P&S. Inone embodiment, the green composition includes the binder composition,as described above, and at least one inorganic powder selected from ametal powder, a metal oxide powder, a non-metallic powder and a ceramicpowder. In one embodiment, the green composition includes the bindercomposition in an amount in the range from about 1 vol % to about 10 vol% and the inorganic powder or powders in an amount from about 99 vol %to about 90 vol %, or the binder composition from about 2 vol % to about5 vol % and the inorganic powder from about 98 vol % to about 95 vol %,or binder composition at about 2.5 vol % and the inorganic powder atabout 97.5 vol %.

Inorganic Powders

Inorganic powders used in the present invention include metallic, metaloxide, intermetallic and/or ceramic powders. The powders may be oxidesor chalcogenides of metallic or nonmetallic elements. An example ofmetallic elements which may be present in the inorganic powders includecalcium, magnesium, barium, scandium, titanium, titanium hydride,titanium Al6—V4, vanadium, chromium, manganese, iron, cobalt, nickel,copper, zinc, yttrium, niobium, molybdenum, ruthenium, rhodium, silver,cadmium, lanthanum, actinium, gold, alloys or combinations of two ormore thereof. In one embodiment, the inorganic powder may contain rareearth or ferromagnetic elements. The rare earth elements include thelanthanide elements having atomic numbers from 57 to 71, inclusive andthe element yttrium, atomic number 39.

Ferromagnetic metals, for purposes of this invention, include iron,nickel, cobalt and numerous alloys containing one or more of thesemetals. In another embodiment the metals are present as alloys of two ormore of the aforementioned elements. In particular, pre-alloyed powderssuch as low alloy steel, bronze, brass and stainless steel as well asnickel-cobalt based super alloys may be used as inorganic powders.

The inorganic powders may comprise inorganic compounds of one or more ofthe above-described metals. The inorganic compounds include ferrites,titanates, nitrides, carbides, borides, fluorides, sulfides, hydroxidesand oxides of the above elements. Specific examples of the oxide powdersinclude, in addition to the oxides of the above-dentified metals,compounds such as beryllium oxide, magnesium oxide, calcium oxide,strontium oxide, barium oxide, lanthanum oxide, gallium oxide, indiumoxide, selenium oxide, zinc oxide, aluminum oxide, silica, zirconia,mullite, mica, indium tin oxide, rare earth oxides, titania, yttria,etc. Specific examples of oxides containing more than orie metal,generally called double oxides, include perovskite-type oxides such asNaNbO₃, SrZro₃, PbZrO₃, SrTiO₃, BaZrO₃, BaTiO₃; spinel-type oxides suchas MgAl₂O₄, ZnAl₂O₄, CoAl₂O₄, NiAl₂O₄, NiCr₂O₄, FeCr₂O₄, MgFe₂O₄,ZnFe₂O₄, etc.; illmenite-types oxides such as MgTiO₃ MnTiO₃, FeTiO₃,CoTiO₃, ZnTiO₃, LiTaO₃, etc.; and gamet-type oxides such as Gd₃Ga₅O₁₂and rare earth-iron gamet represented by Y₃Fe₅O₁₂. The inorganic powdermay also be a clay. Examples of clays include kaolinite, nacrite,dickite, montmorillonite, montronite, spaponite, hectorite, etc.

An example of non-oxide powders include carbides, nitrides, borides andsulfides of the metals described above. Specific examples of thecarbides include SiC, TiC, WC, TaC, HfC, ZrC, AlC; examples of nitridesinclude Si₃N₄, AlN, BN and Ti₃N₄; and borides include TiB₂, ZrB₂, B₄Cand LaB₆. In one embodiment, the inorganic powder is silicon nitride,silicon carbide, zirconia, alumina, aluminum nitride, barium ferrite,barium-strontium ferrite or copper oxide. In another embodiment, thepowder is a semiconductor, for example, GaAs, Si, Ge, Sn, AlAs, AlSb,GaP, GaSb, InP, InAs, InSb, CdTe, HgTe, PbSe, PbTe, and any of the manyother known semiconductors. In another embodiment, the inorganic powderis alumina or clay.

Acids for Reaction with Guanidine

The acidic compounds useful in making the reaction product of guanidineand an acid of the present invention include carboxylic acids, sulfonicacids, phosphorus acids, phenols or mixtures of two or more thereof.Preferably, the acidic organic compounds are carboxylic acids orsulfonic acids. The carboxylic and sulfonic acids may have substituentgroups derived from the above described polyalkenes. As noted above, thepresently most preferred guanidine compounds are guanidine stearate andguanidine 2-ethyl hexanoate. However, other acids may be used, asdescribed herein.

The carboxylic acids may be aliphatic or aromatic, mono- orpolycarboxylic acid or acid-producing compounds. The acid-producingcompounds include anhydrides, lower alkyl esters, acyl halides, lactonesand mixtures thereof unless otherwise specifically stated.

Illustrative fatty carboxylic acids include palmitic acid, stearic acid,myristic acid, oleic acid, linoleic acid, behenic acid,hexatriacontanoic acid, tetrapropylenyl-substituted glutaric acid,polybutenyl (Mn=200-1,500, preferably 300-1,000)-substituted succinicacid, polypropylenyl (Mn=200-1,000, preferably 300-900)-substitutedsuccinic acid, octadecyl-substituted adipic acid, 9-methylstearic acid,stearyl-benzoic acid, eicosane-substituted naphthoic acid,dilauryl-decahydronaphthalene carboxylic acid, mixtures of these acids,and/or their anhydrides. Aliphatic fatty acids include the saturated andunsaturated higher fatty acids containing from about 8 to about 30carbon atoms. Illustrative of these acids are octanoic acid,2-ethyl-hexanoic acid, decanoic acid, lauric acid, palmitic acid, oleicacid, linoleic acid, linolenic acid, oleostearic acid, stearic acid,myristic acid, and undecalinic acid, alpha-chlorostearic acid,alpha-nitrolauric acid, behenic acid (docosanoic acid), tetracosanoicacid, hexacosanoic acid, and octacosanoic acid. Branched fatty acids,both saturated and unsaturated, in the range from about 6 to about 25carbon atoms are included. Such branched fatty acids include versaticacids, available from Shell Chemicals. For example, Shell Chemicalproduces a versatic acid known as Monomer Acid, which is the distilledproduct obtained during the manufacture of tall oil-based dimer acid.Monomer Acid is a mixture of both branched and straight-chainpredominantly C₁₈ mono fatty acids. One example is Versatic 10, asynthetic saturated monocarboxylic acid of highly branched structurecontaining ten carbon atoms. Its structure may be represented as;

where R₁, R₂ and R₃ are alkyl groups at least one of which is alwaysmethyl.

The sulfonic acids useful in making the guanidine wetting agents includethe sulfonic and thiosulfonic acids. Generally they are salts ofsulfonic acids. The sulfonic acids include the mono- or polynucleararomatic or cycloaliphatic compounds. The oil-soluble sulfonates can berepresented for the most part by one of the following formulae:R⁷—T—(SO₃)_(d) and R⁸—(SO₃)_(e), wherein T is a cyclic nucleus such as,for example, benzene, naphthalene, anthracene, diphenylene oxide,diphenylene sulfide, petroleum naphthenes, etc.; R⁷ is an aliphaticgroup such as alkyl, alkenyl, alkoxy, alkoxyalkyl, etc.; the R⁷ groupcombined with the T group contains a total of at least about 15 carbonatoms; R⁸ is an aliphatic hydrocarbyl group containing at least about 15carbon atoms and d and e are each independently an integer from 1 toabout 3, preferably 1. Examples of R⁸ are alkyl, alkenyl, alkoxyalkyl,carboalkoxyalkyl, etc. Specific examples of R⁸ are groups derived frompetrolatum, saturated and unsaturated paraffin wax, and theabove-described polyalkenes. The groups T, R⁷, and R⁸ in the aboveformulae can also contain other inorganic or organic substituents inaddition to those enumerated above such as, for example, hydroxy,mercapto, halogen, nitro, amino, nitroso, sulfide, disulfide, etc. Inthe above formulae, d and e are at least 1.

Illustrative examples of these sulfonic acids includemonoeicosane-substituted naphthalene sulfonic acids, dodecylbenzenesulfonic acids, didodecylbenzene sulfonic acids, dinonylbenzene sulfonicacids, cetylchlorobenzene sulfonic acids, dilauryl beta-naphthalenesulfonic acids, the sulfonic acid derived by the treatment ofpolybutenyl, having a number average molecular weight (Mn) in the rangeof about 500, preferably about 800 to about 5000, preferably about 2000,more preferably about 1500, with chlorosulfonic acid, nitronaphthalenesulfonic acid, paraffin wax sulfonic acid, cetyl-cyclopentane, sulfonicacid, laurykcyclohexane sulfonic acids, polyethylenyl (Mn=300-1,000,preferably 750) sulfonic acids, etc. Normally the aliphatic groups willbe alkyl and/or alkenyl groups such that the total number of aliphaticcarbons is at least about 8, preferably at least 12.

A preferred group of sulfonic acids are mono-, di-, and tri-alkylatedbenzene and naphthalene (including hydrogenated forms thereof) sulfonicacids. Illustrative of synthetically produced alkylated benzene andnaphthalene sulfonic acids are those containing alkyl substituentshaving from about 8 to about 30 carbon atoms, preferably about 12 toabout 30 carbon atoms, and advantageously about 24 carbon atoms. Suchacids include di-isododecyl-benzene sulfonic acid,polybutenyl-substituted sulfonic acid, polypropylenyl-substtutedsulfonic acids of Mn=300-1000, preferably 500-700, cetylchlorobenzenesulfonic acid, di-cetylnaphthalene sulfonic acid, di-lauryldiphenylethersulfonic acid, diisononylbenzene sulfonic acid, di-isooctadecylbenzenesulfonic acid, stearylnaphthalene sulfonic acid, and the like.

The production of sulfonates from detergent manufactured by-products byreaction with, e.g., SO₃, is well known to those skilled in the art.See, for example, the article “Sulfonates” In Kirk-Othmer “Encyclopediaof Chemical Technology”, Second Edition, Vol. 19, pp. 291 et seq.published by John Wiley & Sons, New York (1969).

The phosphorus-containing acids useful in making the guanidine wettingagents include any phosphorus acids such as phosphoric acid or esters;and thiaphosphorus acids or esters, including mono and dithiophosphorusacids or esters. Preferably, the phosphorus acids or esters contain atleast one, preferably two, hydrocarbyl groups containing from 1 to about50 carbon atoms, typically 1, preferably 3, more preferably about 4 toabout 30, preferably to about 18, more preferably to about 8.

In one embodiment, the phosphorus-containing acids are dithiophosphoricacids which are readily obtainable by the reaction of phosphoruspentasulfide (P₂S₅) and an alcohol or a phenol. The reaction involvesmixing at a temperature of about 20° C. to about 200° C. four moles ofalcohol or a phenol with one mole of phosphorus pentasulfide. Hydrogensulfide is liberated in this reaction. The oxygen-containing analogs ofthese acids are conveniently prepared by treating the dithioic acid withwater or steam which, in effect, replaces one or both of the sulfuratoms with oxygen.

In one embodiment, the phosphorus-containing acid is the reactionproduct of the above polyalkenes and phosphorus sulfide. Usefulphosphorus sulfide-containing sources include phosphorus pentasulfide,phosphorus sesquisulfide, phosphorus heptasulfide and the like.

The reaction of the polyalkene and the phosphorus sulfide generally mayoccur by simply mixing the two at a temperature above 80° C., preferablybetween 100° C. and 300° C. Generally, the products have a phosphoruscontent from about 0.05% to about 10%, preferably from about 0.1% toabout 5%. The relative proportions of the phosphorus sulfide to theolefin polymer is generally from 0.1 part to 50 parts of the phosphorussulfide per 100 parts of the olefin polymer.

The phenols useful in making the guanidine wetting agents may berepresented by the formula (R)_(f)—Ar—(OH)_(g), wherein R and Ar aredefined above; f and g are independently numbers of at least one, thesum of f and g being in the range of two up to the number ofdisplaceable hydrogens on the aromatic nucleus or nuclei of Ar.Preferably, f and g are independently numbers in the range of 1 to about4, more preferably 1 to about 2. R and f are preferably such that thereis an average of at least about 8 aliphatic carbon atoms provided by theR groups for each phenol compound. Examples of phenols includeoctylphenol, nonylphenol, propylene tetramer substituted phenol,tri(butene)-substituted phenol, polybutenyl-substituted phenol andpolypropenyl-substituted phenol.

Plasticizers

In one embodiment, a plasticizer is added to the binder composition.Plasticizers may be added to the compositions to provide more workablecompositions. Examples of plasticizers normally utilized in inorganicformulations include butyl stearate, dioctyl phthalate, dibutylphthalate, benzyl butyl phthalate and phosphate and citrate esters.Other known plasticizers may be used.

The amount of plasticizer may be suitably selected, depending on theproperties desired. In one embodiment, the plasticizer is present in anamount from 0.1 wt % to about 25 wt % of the binder composition. Inanother embodiment, the plasticizer may be present in an amount fromabout 5 wt % to about 20 wt %, or from about 5 wt % to about 25 wt %, orfrom about 10 wt % to about 20 wt %, or from about 18 wt % to about 22wt % of the binder composition.

When a plasticizer is present, the quantities of the remainingcomponents of the binder composition may be proportionately reduced, orindividual components may be reduced to compensate for the addedplasticizer. For example, in one embodiment, the binder compositioncomprises butyl stearate as a plasticizer in the binder composition, inan amount of about 20 wt % of the binder composition, and the guanidinewetting agent is reduced to about 5 wt % of the binder composition. Inthis embodiment, the remaining components, i.e., the aliphatic polyesterand the bisamide component are present approximately in their usualconcentrations, for example, about 55 wt % polycaprolactone and about 25wt % bisamide. The reduced quantity of guanidine wetting agent maycomprise one or more individual guanidine components, for example,guanidine ethyl hexanoate and guanidine stearate, when both are presentin another embodiment, the guanidine wetting agent is reduced to about0.1 wt %, or to about 0.5 wt %, or to about 1 wt %, or in the range fromabout 1 to about 5 wt %, when a plasticizer is added. In embodiments inwhich the guanidine wetting agent is reduced to about 5 wt % or less,the components of the binder composition other than the plasticizer andguanidine wetting agents may be present in about the same amounts givenabove, or may be reduced proportionately.

Other Additives

Other additives used in prior art binder compositions are not necessarywith the binder composition of the present invention. In one embodiment,no additives beyond the inventive binder composition are used. In oneembodiment, as deemed necessary, small amounts of other materials may beadded to the composition of the present invention. Such other materialsmay include coupling agents, antoxidants, lubricants, dispersants, andelasticizing agents.

Methods

The present invention further relates to a method for forming a part bypowder injection molding, comprising the steps of (a) forming a greencomposition comprising a binder composition and an inorganic powder,wherein the binder composition comprises an aliphatic polyester polymer,an ethylenebisamide wax, a guanidine wetting agent, and an additive and(b) heating the green composition to debind the green composition,wherein the additive accelerates or extends debinding step (b). In oneembodiment, step (b) occurs by reverse debinding of the bindercomposition. In one embodiment, the inorganic powder is selected from ametal powder, a metal oxide powder, an intermetallic powder and aceramic powder.

In one embodiment, the binder composition comprises an aliphaticpolyester polymer, an ethylenebisamide wax, and a guanidine wettingagent. In one embodiment, the binder composition comprises an aliphaticpolyester polymer, an ethylenebisamide wax, and a guanidine wettingagent, with the proviso that the aliphatic polyester polymer does notinclude a polycarbonate polymer. In one embodiment, the bindercomposition comprises an aliphatic polyester polymer, anethylenebisamide wax, and a guanidine wetting agent, with the provisothat the aliphatic polyester polymer does not include a poly(propylene)carbonate polymer. In one embodiment, the binder composition comprisesan aliphatic polyester polymer, an ethylenebisamide wax, and a guanidinewetting agent, with the proviso that the aliphatic polyester polymerdoes not include polycarbonate aliphatic polyesters such as: poly(ethylene carbonate); poly (1,2-propylene carbonate); poly(1,3-propylene carbonate); poly (1,2-butylene carbonate); poly(1,3-butylene carbonate); poly (1,4-butylene carbonate); poly(1,2-pentylene carbonate); poly [1,3-(2,2-dimethyl propylenecarbonate)]; poly (1,5-pentylene carbonate); and poly (1,6-hexylenecarbonate). In such an embodiment which does not include a polycarbonatepolymer, the binder composition may or may not comprise an additivewhich affects the rate of debinding.

In one embodiment, the additive is a debinding accelerator whichaccelerates debinding step (b) as described above. In one embodiment,the debinding accelerator is an organic peroxide as described above. Inone embodiment, the organic peroxide is a dialkyl peroxide as describedabove. In one embodiment, the debinding accelerator is a metal asdescribed above.

In one embodiment, the additive is a debinding extender which extendsdebinding step (b). In one embodiment, the debinding extender is apolymer having a debinding temperature in the range from about 450° C.to about 850° C. as described above. In one embodiment, the debindingextender is at least one of a polypropylene polymer or apolymethacrylate polymer as described above. In one embodiment, thedebinding extender is a polypropylene polymer having a weight averagemolecular weight of about 50,000 as described above. In one embodiment,the debinding extender is a polymethacrylate polymer having a weightaverage molecular weight of about 100,000 as described above.

In one embodiment, the debinding step (b) includes a plurality oftemperature increases to elevated temperatures, and each of the elevatedtemperatures is maintained substantially constant for a period of time.In one embodiment, a first elevated temperature corresponds to thedebinding temperature of the aliphatic polyester polymer, a secondelevated temperature corresponds to the debinding temperature of theethylanebisamide wax, and a third elevated temperature corresponds tothe debinding temperature of the guanidine wetting agent in oneembodiment, the second elevated temperature corresponds to the debindingtemperature of both the ethylenebisamide wax and the guanidine wettingagent in one embodiment, the additive reduces the time for debinding ofthe aliphatic polyester polymer.

In one embodiment, the additive debinds at a fourth elevatedtemperature, the fourth elevated temperature being higher than saidfirst, second and third elevated temperatures, thus extending thedebinding.

In one embodiment, the method further comprises a step of transferringthe flowable green composition into a mold for a part.

In one embodiment, the debinding step (b) comprises heating the part toa temperature at which the binder composition debinds. In oneembodiment, the method further comprises a step of heating the part to atemperature at which the powder is sintered. In one embodiment, thedebinding step (b) occurs by in reverse debinding of the bindercomposition.

In one embodiment, the debinding step (b) comprises heating the greencomposition to a plurality of elevated temperatures to debind the greencomposition by reverse debinding, wherein a first elevated temperaturecorresponds to the debinding temperature of the aliphatic polyesterpolymer, a second elevated temperature corresponds to the debindingtemperature of the ethylenebisamide wax, and a third elevatedtemperature corresponds to the debinding temperature of the guanidinewetting agent.

In one embodiment, the additive is a debinding extender and step (b)further comprises heating to a fourth elevated temperature whichcorresponds to the debinding temperature of the debinding extender,thereby extending the debinding.

In another embodiment, the method comprises steps of transferring thegreen composition into a mold for a part, heating the part to atemperature at which the binder composition debinds, further heating thepart to a temperature at which the powder is sintered to form the part,and then cooling and removing the part from the mold. In anotherembodiment, the transferring step includes heating and injection of thegreen composition into a mold for powder injection molding. In anotherembodiment, the transferring step includes gravity feeding the greencomposition into a mold for press & sinter molding. In anotherembodiment of the method, the heating step is performed as a series oftemperature increases to selected temperatures, in which the selectedtemperatures correspond to debinding temperatures of the components inthe binder composition. In another embodiment, the selected temperaturesare held for a period of time, to allow the component to be deboundprior to increasing the temperature to a debinding temperature ofanother component. In one embodiment of the method, the order ofdebinding is aliphatic polyester polymer first, ethylenebisamide second,guanidine wetting agent third. In one embodiment, the ethylenebisamidewax and the guanidine wetting agent debind substantially simultaneously.In one embodiment, the additive is a debinding extender which completesdebinding subsequent to the completion of debinding of the guanidinewetting agent. In one embodiment, a wicking agent may be used in thedebinding step. In another embodiment, the wicking agent may be used inboth the debinding step and the sintering step. The wicking agent maybe, for example, a fine alumina or zirconia sand.

In one embodiment of the method, the guanidine wetting agent is areaction product of guanidine and an acid selected from organic acid, afatty acid and a strong acid such as an alkyl sulfonic acid. In oneembodiment of the method, the guanidine wetting agent is guanidinestearate. In one embodiment of the method, the guanidine wetting agentis guanidine ethyl hexanoate. In one embodiment of the method, theguanidine wetting agent is guanidine lauryl sulfonate. In oneembodiment, the guanidine wetting agent is a mixture of two or more ofthese.

In one embodiment of the method, the aliphatic polyester polymer has anumber average (Mn) molecular weight in the range from about 60,000 toabout 120,000. In one embodiment of the method, the aliphatic polyesterpolymer has a Mn molecular weight in the range from about 70,000 toabout 90,000. In one embodiment of the method, the aliphatic polyesterpolymer has a Mn molecular weight of about 80,000.

In one embodiment of the method, the additive is a debindingaccelerator, which is an organic peroxide. In another embodiment, thedebinding accelerator is an azo compound. In another embodiment, thedebinding accelerator is an externally applied free radical source. Inone embodiment, the debinding accelerator is a metal, such as atransition metal. In the embodiments of the method including a debindingaccelerator, the debinding accelerator may be any of the debindingaccelerators identified and described hereinabove.

In one embodiment of the method, the additive is a debinding extenderwhich is a polymer. In another embodiment, the debinding extender is apolypropylene polymer. In another embodiment, the debinding extender isa polymethacrylate polymer. In the embodiments of the method including adebinding extender, the debinding extender may be any of the debindingextenders identified and described hereinabove.

In one embodiment, the method employs both a debinding accelerator and adebinding extender. In such an embodiment, since the inorganic powder isa higher-temperature-sintering material, the debinding extender isneeded to assure that the binder composition continues to bind theinorganic powder particles in place until the onset or initiation ofsintering. For the same reason, the initial heating steps which debindthe aliphatic polyester polymer likely do not occur together with anypre-sintering, so, once the green composition has been placed in themold, the low-temperature-sintering components such as the aliphaticpolyester polymer, can be expeditiously debound. For this purpose, thedebinding accelerator may be added.

In one embodiment of the method, the binder composition comprises theguanidine wetting agent in the range from about 5 wt % to about 30 wt %based on the binder composition, the aliphatic polyester polymer in therange from about 30 wt % to about 85 wt % based on the bindercomposition, and the ethylenebisamide wax in the range from about 10 wt% to about 40 wt % based on the binder composition. In one embodiment ofthe method, the additive is a debinding accelerator which is present inthe range from about 0.01 wt % to about 10 wt % of the bindercomposition. In another embodiment of the method, the additive is adebinding extender which is present in the range from about 1 wt % toabout 20 wt % of the binder composition. In one embodiment, both thedebinding accelerator and the debinding extender are present, in theabove proportions.

In one embodiment of the method, the binder composition comprises theguanidine wetting agent in the range from about 10 wt % to about 25 wt %based on the binder composition, the aliphatic polyester polymer in therange from about 40 wt % to about 60 wt % based on the bindercomposition, and the ethylenebisamide wax in the range from about 15 wt% to about 35 wt % based on the binder composition.

When either or both types of the additive are present, the relativeweight percentage of the other three binder components may be adjustedaccordingly. In one embodiment, the relative proportions between theother three components remain the same, each being reducedproportionately. In one embodiment, when a debinding accelerator ispresent, the amount of aliphatic polyester is reduced by an equivalentamount in one embodiment, when a debinding accelerator is present, theamount of aliphatic polyester remains the same, but the amounts of oneor both of the other components are reduced proportionately.

In one embodiment, when the debinding extender is present, the amount ofguanidine wetting agent remains the same, but the amounts of one or bothof the other components are reduced proportionately.

In one embodiment of the method, the binder composition is present in anamount in the range from about 30 vol % to about 60 vol % of the greencomposition and the inorganic powder is present in an amount from about70 vol % to about 40 vol % of the green composition, or the bindercomposition from about 40 vol % to about 50 vol % of the greencomposition and the inorganic powder from about 60 vol % to about 40 vol% of the green composition, or the binder composition at about 35 vol %and the inorganic powder at about 65 vol %.

Preparation of the Binder and Green Compositions

FIG. 1 is a schematic diagram of the steps in a generalized process formaking a part by powder injection molding in accordance with the presentinvention. In a first step 10 an inorganic powder and a bindercomposition according to the present invention are obtained andcombined. In one embodiment, the step of preparing the bindercomposition includes steps of mixing, blending and dispersing thecomponents of the binder composition as needed to prepare a homogenous,or nearly homogenous, mixture of the components in the bindercomposition, in a powder form. The optional ingredients may be added atthis time. In one embodiment, the binder composition and the inorganicpowder are first dry blended to produce a homogenous mix of drymaterials. In one embodiment, the binder composition is micronized to asize similar to that of the inorganic powder with which it will becombined to form the green composition. In one embodiment, the bindercomposition is ground to a particle size in the range from about 10 μmto about 100 μm.

In an optional second step (not shown) the inorganic powder and thebinder composition are combined in a premixing of the green composition.The optional premixing step may include mixing in, e.g., a ball mill. Inthis optional step, additional components, if used, may be added andblended into the mixture as desired.

In a step 20 the components of the green composition are fed into a twinscrew compounding extruder. In the step 20, while passing through thetwin screw compounding extruder, the components of the green compositionare subjected to a high shear for effectively combining the inorganicpowder and binder composition. While the use of a twin screw extruder ispreferred, it is not necessary to the process of the invention that atwin screw extruder be used. The twin screw extruder provides areliable, consistent, suitably thorough mixing of the ingredients. Otherknown and available mixing methods may be employed to achieve the mixingof the components of the green composition. For example, suitablythorough mixing may be attained with a sigma blade mixer, a Banburymixer, a double planetary mixer, a single screw mixer, a paddlecompounder or a shear roll compounder.

In one embodiment, the output from the twin screw compounding extruderis a string of the green composition, which is then fed to a pelletizer.In one embodiment, the output from the twin screw compounding extruderis pelletized by a pelletizing apparatus directly attached to theextruder apparatus. Forming the green composition into pelletsfacilitates handling, both for immediate and for subsequent use. Themixing in the twin screw compounding extruder in the step 20 facilitatesblending the various green compositions as may be required forparticular applications. The mixing in the twin screw compoundingextruder in the step 20 combines, compounds and pelletizes the greencomposition. The pellets formed by the step 20 may be cooled and storedfor later use, or may be used immediately with or without cooling.

In one embodiment of the step 20 the binder composition is dry blendedwith the inorganic powder prior to feeding to the twin screw compoundingextruder, and the blended components of the green composition are fedinto the extruder together. In one embodiment, the binder compositionand inorganic powder components of the green composition are fedseparately into the twin screw compounding extruder. In one embodiment,the binder composition is fed into the twin screw compounding extruderat a first point, and the inorganic powder component is fed in at asecond point, downstream from the first point.

Referring again to FIG. 1, in an injection molding step 30, the pelletsof the green composition are heated, melted, mixed and injected into amold having the desired shape of the part of interest. The part formedat this stage is known as a green part or a compact for a part. In oneembodiment, the molten green composition is injected into the mold at apressure in the range from about 100 psi (about 7 Kg/cm²) to about 2000psi (about 140 Kg/cm²). In one embodiment, the molten green compositionis injected into the mold at a pressure of about 800 psi (about 56Kg/cm²). In the injection step 30, pellets having different greencompositions may be blended. Following the injection step 30, the greenpart is cooled and released from the mold.

In one embodiment, the pellets are fed into a hopper and thence into ahorizontal injection molding machine. In one embodiment, the injectionmolding machine is a standard injection molding machine used forinjection molding parts in known processes.

In one embodiment, the green part has a green strength in the range ofabout 800 psi (about 56 Kg/cm²) to about 12,000 psi (about 844 Kg/cm²),or from about 2000 psi (about 140 Kg/cm²) to about 8000 psi (about 562Kg/cm²), or from about 4000 psi (about 281 Kg/cm²) to about 6000 psi(about 422 Kg/cm²).

The green part is then transferred to a debinding/sintering oven, inwhich one or more steps of debinding 40 are carried out. In oneembodiment, the debinding step 40 includes a plurality of temperatureincreases to elevated temperatures. In one embodiment of the debindingstep 40, each of the elevated temperatures are maintained constant for aperiod of time. In one embodiment of the debinding step 40, the elevatedtemperatures correspond to temperatures at which individual ingredientsof the binder composition are debound. In one embodiment of thedebinding step 40, a first elevated temperature corresponds to thedebinding temperature of the aliphatic polyester polymer, a secondelevated temperature corresponds to the debinding temperature of theethylenebisamide wax, and a third elevated temperature corresponds tothe debinding temperature of the guanidine wetting agent in oneembodiment of the debinding step 40, the third elevated temperature ishigher than the second elevated temperature, and the second elevatedtemperature is higher than the first elevated temperature. In oneembodiment, the second and third elevated temperatures are approximatelythe same, the ethylenebisamide wax and the guanidine wetting agentdebinding substantially simultaneously.

In one embodiment, when the additive is present in the form of adebinding extender, the part is heated to a fourth or further elevatedtemperature, and may be held at that temperature for a period of time.The fourth or further elevated temperature corresponds to the debindingtemperature of the debinding extender. The fourth or further elevatedtemperature is higher than the third elevated temperature. The fourth orfurther elevated temperature may be in the range from about 450° C. toabout 850° C.

Following the debinding step 40, the green part is subjected to a step50 of sintering. The sintering step 50 may be performed in the same ovenin which the debinding step 40 was performed, or the green part may bemoved to a separate sintering oven for the sintering step 50.

A twin screw extruder may be used for extrusion of the bindercomposition. In one embodiment, the twin screw extruder is a Leistritztwin screw extruder as disclosed in U.S. Pat. Nos. 6,093,761 and6,204,316, the disclosure of which is incorporated by reference hereinfor its teachings relating to the twin screw extruder.

EXAMPLES

The following exemplary formulations and processes are intended toprovide a better understanding of the invention, and are not intended aslimiting the scope of the invention. The scope of the invention isdescribed in the appended claims.

Example 1

A green composition comprising a binder composition and an inorganicpowder comprising 98% carbonyl iron doped with 2% nickel as a sinteringaid, according to the present invention, is prepared as follows.

poly(propylene carbonate) 59.43 wt % ethylenebisstearamide ACRAWAX ®C25.15 wt % guanidine ethyl hexanoate  8.49 wt % guanidine stearate  6.93wt % Total 100.0  wt %The above binder composition does not include either additive, thedebinding accelerator or the debinding extender. The binder compositionis prepared by combining the ingredients in a twin screw compoundingextruder, heating to about 120-130° C. until the mixture issubstantially homogenous, and then pelletizing the binder compositionin, e.g., a strand cutter pelletizing apparatus. This binder compositionis designated APEX™ 201.

The ingredients for the green composition comprise 59 vol % carbonyliron/nickel and 41 vol % of pellets of the above binder composition, thegreen composition components are combined, compounded and pelletized ina twin screw compounding extruder such as described above. Expressed ona weight basis, the green composition comprises 91 wt % carbonyl iron/Niand 9 wt % of the above binder composition. After the green compositionis thoroughly compounded, it is extruded and pelletized. The pellets aresubsequently fed into an injection molding machine, and injected into amold. The debinding profile of Example 1 is shown below in Table 1 andin FIG. 2.

TABLE 1 Step Time, Elapsed No. Action in Step min. Time, min. 21 Heatfrom RT @ 75° C./hr to 110° C. 68 68 22 Soak (hold) @ 110° C. 60 128 23Heat from 110° C. @ 75° C./hr to 140° C. 18 146 24 Heat from 140° C. @100° C./hr to 190° C. 40 186 25 Soak (hold) @ 190° C. 60 246 26 Heatfrom 190° C. @ 150° C./hr to 425° C. 94 340 27 Soak (hold) @ 425° C. 60400 28 Heat from 425° C. to sintering temperature

In FIG. 2 and Table 1, the poly(propylene carbonate) is debound in steps23, 24 and 25, a total of 118 minutes. The ethylenebisstearamide isdebound in step 26. The guanidine wetting agent is debound in steps 26and 27. Following substantially complete debinding, and the end of step27, at an elapsed debinding time of 400 minutes, the part is sintered byheating in step 28 at the rate of 300° C./hr to a sintering temperatureof 1425° C. In the steps 21 to 26, the atmosphere is hydrogen at apressure of 780 torr. In the steps 27 and 28, the chamber is held undera vacuum of about 10⁻⁶ torr.

Example 2

A green composition comprising a binder composition and silica,according to the present invention, is prepared as follows.

poly(propylene carbonate) 51.43 wt % ethylenebisstearamide ACRAWAX ®C29.15 wt % guanidine ethyl hexanoate 9.48 wt % guanidine stearate 9.93wt % 2,5-dimethyl-2,5-di(t-butylperoxy)hexane 0.01 wt % Total 100.00The binder composition is prepared by combining the ingredients in atwin screw compounding extruder, heating to about 100° C. for about 10minutes, until the mixture is substantially homogenous, and thenpelletizing the binder composition in, e.g., a strand cutter pelletizingapparatus. This binder composition is designated APE™ 203.

The ingredients for the green composition comprise 65 vol % silica and35 vol % of pellets of the above binder composition. These componentsare combined, compounded and pelletized in a twin screw compoundingextruder as described above. Expressed on a weight basis, the greencomposition comprises 77 wt % silica and 23 wt % of the above bindercomposition. After the green composition is thoroughly compounded, it isextruded and pelletized. The pellets are subsequently fed into aninjection molding machine, and injected into a mold. The debindingprofile of Example 2, in which the additive is present in the form of adebinding accelerator, is shown below in Table 2 and in FIG. 3.

TABLE 2 Step Time, Elapsed No. Action in Step min. Time, min. 21 Heatfrom RT @ 75° C./hr to 110° C. 68 68 22 Soak (hold) @ 110° C. 20 88 23Heat from 110° C. @ 100° C./hr to 190° C. 54 142 24 Soak at 190° C. 30172 25 Heat from 190° C. @ 150° C./hr to 425° C. 94 266 26 Soak (hold) @425° C. 30 296 27 Heat from 425° C. to sintering temperatureIn FIG. 3 and Table 2, the poly(propylene carbonate) is debound in steps23 and 24, a total of 84 minutes. As can be observed by comparison ofsteps 23 and 24 in FIG. 3 and Table 2 with steps 23, 24 and 25 in FIG. 2and Table 1, the time for debinding the poly(propylene carbonate) issubstantially reduced, from 118 to 84 minutes, thus reducing the overalldebinding time. The ethylenebisstearamide is debound in step 25. Theguanidine wetting agent is debound in steps 26 and 27. Followingsubstantially complete debinding, at the end of step 27 at an elapseddebinding time of 296 minutes, the part is sintered by heating in step27 at the rate of 300° C./hr to a sintering temperature of 1425° C. Inthe steps 21 to 25, the atmosphere is hydrogen at a pressure of 780torr. In the steps 26 and 27, the chamber is held under a vacuum ofabout 10⁻⁶ torr. Thus, by addition of the organic peroxide debindingaccelerator, the pre-sintering time is reduced from 400 minutes to 296minutes. This time may be further reduced by increasing the rate oftemperature increase in step 21.

Example 3

A green composition comprising a binder composition and titanium,according to the present invention, is prepared as follows.

poly(propylene carbonate) Q-PAC ™ 40 52.43 wt % ethylenebisstearamideACRAWAX ®C 20.15 wt % guanidine ethyl hexanoate 8.49 wt % guanidinestearate 6.94 wt % atactic polypropylene M_(n) ≅ 50,000 12.00 wt % Total100.00 wt %The binder composition is prepared by combining the ingredients in atwin screw compounding extruder, heating to about 100° C. for about 10minutes, until the mixture is substantially homogenous, and thenpelletizing the binder composition in, e.g., a strand cutter pelletizingapparatus. This binder composition is designated APEX™ 204.

The ingredients for the green composition comprise 59 vol % titanium and41 vol % of pellets of the above binder composition. These componentsare combined, compounded and pelletized in a twin screw compoundingextruder as described above. Expressed on a weight basis, the greencomposition comprises 86 wt % titanium and 14 wt % of the above bindercomposition. After the green composition is thoroughly compounded, it isextruded and pelletized. The pellets are subsequently fed into aninjection molding machine, and injected into a mold. The debindingprofile of Example 3, in which the additive is present in the form of adebinding extender, is shown below in Table 3 and in FIG. 4.

TABLE 3 Step Time, Elapsed No. Action in Step min. Time, min. 21 Heatfrom RT @ 75° C./hr to 110° C. 68 68 22 Soak (hold) @ 110° C. 60 128 23Heat from 110° C. @ 75° C./hr to 140° C. 18 146 24 Heat from 140° C. @100° C./hr to 190° C. 40 186 25 Soak (hold) @ 190° C. 60 246 26 Heatfrom 190° C. @ 150° C./hr to 425° C. 94 340 27 Soak (hold) @ 425° C. 60400 28 Heat from 425° C. @ 150° C./hr to 560° C. 65 465 29 Soak (hold) @560° C. 50 515 30 Heat from 560° C. to sintering temperatureIn FIG. 4 and Table 3, the poly(propylene carbonate) is debound in steps24 and 25. The ethylenebisstearamide is debound in step 26. Theguanidine wetting agent is debound in steps 26 and 27. The debindingextender, atactic polypropylene having a number average molecular weight(M_(n)) of about 50,000, is debound in steps 28 and 29. As can beobserved from a comparison of the debinding profile of FIG. 4 and Table3 with that of FIG. 2 and Table 1, the debinding extender portion of thebinder composition remains present at a higher temperature and for alonger period, until it is debound at a temperature of about 560° C.,after an elapsed time of 515 minutes. This is a substantially highertemperature and longer time than would be observed for a bindercomposition such as that of Examples 1 and 2, which do not include adebinding extender. Following substantially complete debinding, and theend of step 29, at an elapsed debinding time of 580 minutes, the part issintered by heating in step 30 at the rate of 300° C./hr to a sinteringtemperature of 1425° C. In the steps 21 to 26, the atmosphere ishydrogen at a pressure of 780 torr. In the steps 27-30, the chamber isheld under a vacuum of about 10⁻⁶ torr.

Example 4

A green composition comprising a binder composition and zirconia,according to the present invention, is prepared as follows.

The binder composition used in the green composition is as follows:

poly(propylene carbonate) Q-PAC ™ 40 50.43 wt % ethylenebisstearamideACRAWAX ®C 25.14 wt % guanidine ethyl hexanoate 6.48 wt % guanidinestearate 5.94 wt % 2,5-dimethyl-2,5-di(t-butylperoxy)hexane 0.01 wt %atactic polypropylene M_(n) ≅ 50,000 12.00 wt % TOTAL 100.00 wt %

The binder composition is prepared by combining the ingredients in atwin screw compounding extruder, heating to about 100° C. for about 10minutes, until the mixture is substantially homogenous, and thenpelletizing the binder composition in, e.g., a strand cutter pelletizingapparatus. This binder composition is designated APEX™ 205.

The ingredients for the green composition comprise 65 vol % zirconia and35 vol % of pellets of the above binder composition. These componentsare combined, compounded and pelletized in a twin screw compoundingextruder as described above. Expressed on a weight basis, the greencomposition comprises 88 wt % zirconia and 12 wt % of the above bindercomposition. After the green composition is thoroughly compounded, it isextruded and pelletized. The pellets are subsequently fed into aninjection molding machine, and injected into a mold. The debindingprofile of Example 4, in which the additive is present in the form ofboth a debinding accelerator and a debinding extender, is shown below inTable 4 and in FIG. 5.

TABLE 4 Step Time, Elapsed No. Action in Step min. Time, min. 21 Heatfrom RT @ 75° C./hr to 110° C. 68 68 22 Soak (hold) @ 110° C. 20 88 23Heat from 140° C. @ 100° C./hr to 190° C. 54 142 24 Soak (hold) @ 190°C. 30 172 25 Heat from 190° C. @ 150° C./hr to 425° C. 94 266 26 Soak(hold) @ 425° C. 30 296 27 Heat from 425° C. @ 150° C./hr to 560° C. 65361 28 Soak (hold) @ 560° C. 50 411 29 Heat from 560° C. to sinteringtemperatureIn FIG. 5 and Table 4, the poly(propylene carbonate) is debound in steps23 and 24, a total of 118 minutes. As can be observed by comparison ofsteps 23 and 24 in FIG. 6 and Table 4 with steps 23-25 in FIG. 2 andTable 1, the time for debinding the poly(propylene carbonate) issubstantially reduced, from 118 to 84 minutes, thus reducing the overalldebinding time. The ethylenebisstearamide is debound in step 25. Theguanidine wetting agent is debound in steps 26 and 27. The debindingextender, atactic polypropylene having a number average molecular weight(M_(n)) of about 50,000, is debound in steps 27 and 28. As can beobserved from the debinding profile, the debinding extender portion ofthe binder composition remains present at a higher temperature and for alonger period, until it is debound at a temperature of about 560° C.,after an elapsed time of 411 minutes. This is a substantially highertemperature and longer time than would be observed for a bindercomposition such as that of Examples 1 and 2, which do not include adebinding extender. Following substantially complete debinding, and theend of step 29, at an elapsed debinding time of 411 minutes, the part issintered by heating in step 29 at the rate of 300° C./hr to a sinteringtemperature of 1425° C., and holding. In the steps 21 to 25, theatmosphere is hydrogen at a pressure of 780 torr. In the steps 26-29,the chamber is held under a vacuum of about 10⁻⁶ torr.

Examples 5-19

The following Examples 5-19 provide further disclosure of the presentinvention. In each of the following Examples 5-19, the greencompositions were prepared as described above and in the quantitiesshown in the following tables. In each of Examples 5-19, the aliphaticpolyester polymer was polycaprolactone, specifically TONE® P787 brand ofhigh molecular weight caprolactone polymer, obtained from Union CarbideCorporation, Danbury, Conn. The Mn molecular weight of the P787polycaprolactone used in Examples 5-19 was about 80,000.

In each of Examples 5-19, except as specifically noted, the same generaldebinding regime was followed, in which a two-stage debinding process isused. In Stage 1, the green part is partially debound to yield a brownpart. The brown part may be moved to a separate apparatus in which Stage2 of debinding and the sintering steps are carried out. In Stage 2, thedebinding of the brown part is completed, and is followed immediately,in the same apparatus, by the sintering step. It is noted that, althoughin the present embodiment the Stage 1 debind is carried out in aseparate apparatus from that used for the Stage 2 debind and sintering,this is not necessarily so; the same apparatus may be used for theentire debinding and sintering. Similarly, the brown part is notnecessarily removed or moved, and the apparatus need not be cooled down,following the Stage 1 debinding. Thus, in one embodiment, the Stage 1and Stage 2 debind cycles, and the sintering cycle, all may be carriedout in a single apparatus in one continuous process.

Thus, except as specifically noted, the following debinding regime wasemployed:

Stage 1 Debind Cycle:

The Stage 1 debinding process used for parts made according to Examples5-19 varies depending on the size and thickness of the parts. For bothsize parts, the debind cycle takes place in a first debind oven, in anappropriate atmosphere, as disclosed in more detail elsewhere herein.For parts having a small size and a thickness from about {fraction(1/16)} inch (about 1.6 mm) to about ⅛ inch (about 3.2 mm), thefollowing Stage 1 debind cycle, Stage 1A, is used:

Stage 1A Debind Cycle:

-   -   1. Ramp temperature to 140° C. at apparatus maximum rate.    -   2. Ramp temperature from 140° C. to 260° C. at 20° C./ hour (6        hr. ramp).    -   3. Hold at260° C. for 1 hour.    -   4. Ramp temperature from 260° C. to 300° C. at apparatus maximum        rate.    -   5. Hold at 300° C. for 1 hour, then cool down.        Thus, the total time for Stage 1A is approximately 8 hours.

For heavier parts having a thickness from about ⅛ inch (about 3.2 mm) toabout ½ inch (about 12.5 mm), the following Stage 1 debind cycle, Stage1B, is used:

Stage 1B Debind Cycle:

-   -   1. Ramp temperature to 140° C. at apparatus maximum rate.    -   2. Ramp temperature from 140° C. to 260° C. at 20° C./ hour (6        hr. ramp).    -   3. Hold at 260° C. for 1 hour.    -   4. Ramp temperature from 260° C. to 300° C. at apparatus maximum        rate.    -   5. Ramp temperature from 300° C. to 320° C. at linear rate over        2 hours.    -   6. Hold at 320° C. for 1 hour, then cool down.        Thus, the total time for Stage 1B is approximately 10 hours. For        heavy or thicker parts, it may be necessary to extend the hold        times, to assure complete debinding. As noted above, the part        obtained from the Stage 1 debinding is referred to as a brown        part. The brown part is removed from the debinding apparatus        following the Stage 1 debinding. When the Stage 2 debinding and        sintering are to be carried out, the brown part is placed in the        sintering apparatus for the Stage 2 of debinding and subsequent        sintering.        Stage 2 Debind Cycle:    -   1. Apply vacuum to approximately 100 microns (0.1 mm) Hg.    -   2. Introduce argon gas or other appropriate gas at approximately        30 SCFH (850 l/hr).    -   3. Heat at 5.5° C./min to 204° C.; hold for 30 minutes.    -   4. Heat at 5.5° C./min to 249° C.; hold for 60 minutes.    -   5. Heat at 16.7° C./min to 426° C.; hold for 15 minutes.    -   6. If sintering atmosphere is other than argon, reapply vacuum        to approximately 100 microns (0.1 mm) Hg, then introduce        sintering atmosphere at approximately 30 SCFH (850 l/hr). If        sintering atmosphere is argon, begin sintering process without        reapplying vacuum.

As will be understood by those of skill in the art, the foregoingdebinding conditions are exemplary only, and may be varied as requiredin order to adjust to different debinding compositions. For example,while each of the aliphatic polyester polymers disclosed herein has amelting point or glass transition temperature (Tg) of less than about140° C., the exact melting point or Tg varies among the aliphaticpolyester polymers disclosed, and the debinding temperatures and timesmay have to be adjusted somewhat accordingly. The debinding temperaturesand times shown in the Examples 5-19 are believed to be the optimum forthe particular materials used in each such Example.

Since the sintering conditions vary according to the material beingsintered, the appropriate sintering conditions are indicated for eachExample separately. As with the debinding conditions, it will beunderstood that these conditions are exemplary only, and, while they arebelieved to be the optimum for the particular combination of materialsin each respective Example, the optimum conditions may vary fordifferent materials, and may be selected as appropriate.

In the following examples, under “Loading”, the left-hand columncontains the percentage by weight of each component of the green part.The right-hand column contains the percentage by volume for theinorganic powder (upper value) and for the binder composition as a whole(lower value). Thus, for example, in Example 5, the silica compositionincludes from 58-62 vol. % of silica and 42-38 vol. % of a bindercomposition composed of the four ingredients listed after “silica” inthe “Component” column. The ranges in the vol. % values result fromvariations in particle size. In the following examples, the “Support” isthe solid support upon which the brown part rests during sintering.

Example 5

Silica Composition (1-150 μm particle size) Loading Component Wt. % Vol.% Sintering Conditions Heat Rate, ° C./min 5 Silica 78.19 58-62 SinterTemp., ° C. 1080 UCAR 787 8.50 Sinter Time, min. 120 Acrawax C 5.4542-38 Atmosphere air Guanidine Stearate 5.89 Support Al₂O₃ Guanidine 2-1.96 Ethylhexanoate Total 100.00 100.00

Example 6

Tungsten Alloy Composition (0.2-4.8 μm particle size) Loading ComponentWt. % Vol. % Sintering Conditions Heat Rate, ° C./min 1700 TungstenAlloy 93.78 45-50 Sinter Temp., ° C. 1700 UCAR 787 2.42 Sinter Time,min. 120 Acrawax C 1.55 55-50 Atmosphere H₂ Guanidine Stearate 1.68Support Mo Guanidine 2- 0.57 Ethylhexanoate Total 100.00 100.00

Example 7

Tungsten Alloy Composition (0.2-4.8 μm particle size) Loading ComponentWt. % Vol. % Sintering Conditions Heat Rate, ° C./min 1700 TungstenAlloy 94.509 47-51 Sinter Temp., ° C. 1700 UCAR 787 1.373 Sinter Time,min. 120 Acrawax C 1.703 53-49 Atmosphere H₂ Guanidine Stearate 1.811Support Mo Guanidine 2- 0.604 Ethylhexanoate Total 100.00 100.00

Example 8

316L Stainless Steel Composition (0.5-40 μm particle size) LoadingComponent Wt. % Vol. % Sintering Conditions Heat Rate, ° C./min 16.7316L Stainless Steel 92.78 60-64 Sinter Temp., ° C. 1288 UCAR 787 4.29Sinter Time, min. 60 Acrawax C 1.82 40-36 Atmosphere H₂ GuanidineStearate 0.50 Support Al₂O₃ Guanidine 2- 0.61 Ethylhexanoate Total100.00 100.00

Example 9

316L Stainless Steel Composition (0.5-40 μm particle size) LoadingComponent Wt. % Vol. % Sintering Conditions Heat Rate, ° C./min 16.7316L Stainless Steel 93.300 62-66 Sinter Temp., ° C. 1288 UCAR 787 2.613Sinter Time, min. 60 Acrawax C 1.674 38-34 Atmosphere H₂ GuanidineStearate 1.810 Support Al₂O₃ Guanidine 2- 0.603 Ethylhexanoate Total100.00 100.00

Example 10

316L Stainless Steel Composition (0.5-40 μm particle size) LoadingComponent Wt. % Vol. % Sintering Conditions Heat Rate, ° C./min 16.7316L Stainless Steel 93.011 60-65 Sinter Temp., ° C. 1288 UCAR 787 2.726Sinter Time, min. 60 Acrawax C 1.747 40-35 Atmosphere H₂ GuanidineStearate 1.887 Support Al₂O₃ Guanidine 2- 0.629 Ethylhexanoate Total100.00 100.00

Example 11

Titanium 6AI-4V Composition (1.5-125 μm particle size) Loading ComponentWt. % Vol. % Sintering Conditions Heat Rate, ° C./min 5.5 Titanium6Al-4V 83.685 55-59 Sinter Temp., ° C. 982/1371 (2-step sinter) UCAR 7876.362 Sinter Time, min. 30/120 Acrawax C 4.080 45-41 Atmosphere ArgonGuanidine Stearate 4.405 Support La/Mo* Guanidine 2- 1.468Ethylhexanoate Total 100.00 100.00 La/Mo* = lanthanized molybdenumsteel; Al₂O₃ as an alternative

Example 12

Titanium 6AI-4V Composition (0.5-40 μm particle size) Loading ComponentWt. % Vol. % Sintering Conditions Heat Rate ° C./min 5.5 Titanium 6AI-4V87.336 60-65 Sinter Temp., ° C. 982/1371 (2-step sinter) UCAR 787 4.938Sinter Time, min. 30/120 Acrawax C 3.167 40-35 Atmosphere ArgonGuanidine Stearate 3.419 Support La/Mo* Guanidine 2- 1.140Ethylhexanoate Total 100.00 100.00 La/Mo* = lanthanized molybdenumsteel; Al₂O₃ as an alternative

Example 13

Carbonyl Iron/2% Nickel Composition (1.5-6.0 μm particle size) LoadingComponent Wt. % Vol. % Sintering Conditions Heat Rate, ° C./min 15Carbonyl Fe/2% Ni 91.193 55-60 Sinter Temp., ° C. 1250 UCAR 787 2.203Sinter Time, min. 60 Acrawax C 2.730 45-40 Atmosphere H₂ GuanidineStearate 2.905 Support Al₂O₃ Guanidine 2- 0.969 Ethylhexanoate Total100.00 100.00

Example 14

Silica Composition w/Debind Accelerator (1-150 μm particle size) LoadingComponent Wt. % Vol. % Sintering Conditions Heat Rate, ° C./min 5 Silica76.564 58-62 Sinter Temp., ° C. 1080 UCAR 787 8.326 Sinter Time, min.120 Acrawax C 5.339 Atmosphere air Guanidine Stearate 5.767 42-38Support Al₂O₃ Guanidine 2- 1.922 Ethylhexanoate 2,5-dimethyl-2,5- 2.082di(t-butylperoxy) hexane Total 100.00 100.00

Example 15

Tungsten Alloy Composition w/Debind Accelerator (0.2- 4.8 μm particlesize) Loading Component Wt. % Vol. % Sintering Conditions Heat Rate, °C./min 1700 Tungsten Alloy 93.558 45-50 Sinter Temp., ° C. 1700 UCAR 7872.414 Sinter Time, min. 120 Acrawax C 1.547 Atmosphere H₂ GuanidineStearate 1.671 55-50 Support Mo Guanidine 2- 0.569 Ethylhexanoate2,5-dimethyl-2,5- 0.241 di(t-butylperoxy) hexane Total 100.00 100.00

Example 16

Tungsten Alloy Composition w/Debind Extender (0.2- 4.8 μm particle size)Loading Component Wt. % Vol. % Sintering Conditions Heat Rate, ° C./min1700 Tungsten Alloy 94.121 47-51 Sinter Temp., ° C. 1700 UCAR 787 1.367Sinter Time, min. 120 Acrawax C 1.696 Atmosphere H₂ Guanidine Stearate1.804 53-49 Support Mo Guanidine 2- 0.601 Ethylhexanoate Atactic Poly-0.410 propylene (Mn = 50,000) Total 100.00 100.00

Example 17

316L Stainless Steel Composition w/Debind Accelerator (0.2-50 μmparticle size) Loading Component Wt % Vol. % Sintering Conditions HeatRate, ° C./min 16.7 316L Stainless Steel 92.462 60-64 Sinter Temp., ° C.1288 UCAR 787 4.277 Sinter Time, min. 60 Acrawax C 1.809 Atmosphere H₂Guanidine Stearate 0.500 40-36 Support Al₂O₃ Guanidine 2- 0.611Ethylhexanoate Succinic peroxide 0.342 Total 100.00 100.00

Example 18

316L Stainless Steel Composition w/Debind Extender (0.5-50 μm particlesize) Loading Component Wt % Vol. % Sintering Conditions Heat Rate, °C./min 16.7 316L Stainless Steel 92.430 62-66 Sinter Temp., ° C. 1288UCAR 787 2.589 Sinter Time, min. 60 Acrawax C 1.659 Atmosphere H₂Guanidine Stearate 1.793 38-34 Support Al₂O₃ Guanidine 2- 0.597Ethylhexanoate PMMA (Mn = 0.932 120,000) Total 100.00 100.00

Example 19

316L Stainless Steel Composition w/Debind Accelerator (0.5- 50 μmparticle size) Loading Component Wt % Vol. % Sintering Conditions HeatRate, ° C./min 16.7 316L Stainless Steel 92.983 60-65 Sinter Temp., ° C.1288 UCAR 787 2.725 Sinter Time, min. 60 Acrawax C 1.747 Atmosphere H₂Guanidine Stearate 1.886 60-35 Support Al₂O₃ Guanidine 2- 0.598Ethylhexanoate Iron octoate 0.932 Total 100.00 100.00

Example 20

Example 20 provides a further example of the present invention. In thisexample a green composition is formed comprising 93.8 wt % tungstenalloy (e.g., an alloy containing 90 wt % Ti, 6 wt % Al, 4 wt % V) and6.2 wt % of a binder composition. The green composition correspondssubstantially to that shown above in Example 6. In Example 20, amodified first stage debind cycle was employed, as follows:

Debind atmosphere: hydrogen, pressure 780 Torr, flow rate sufficient toprovide approximately 5 atmosphere exchanges per hour in the oven(approximately 70 l/hr).

1. Place part on alumina plate and into over at 160° C.

2. Ramp temperature at linear rate from 160° C. to 220° C. in 2 hours.

3. Hold at 220° C. for 2 hours.

4. Ramp temperature at linear rate from 220° C. to 320° C. in 2 hours.

5. Hold at 320° C. for 2 hours.

6. Cool from 320° C. to room temperature in 2 hours.

Thereafter, the brown part is transferred to the sintering oven, and thetungsten part was sintered at a temperature of 1700° C. for a period of120 minutes in a hydrogen atmosphere.

The parts obtained from examples 5-19 were considered excellent, whenevaluated based on surface finish, shrinkage, porosity and density. Thefollowing is a brief indication of the density which was obtained withthe following metals:

Material Obtained Density Standard Industry Density 17-4 Stainless Steel98%+ 92-98% 316L Stainless Steel 99%+ 92-98% Tungsten 98%+ (custom - noindustry standard)

As an example of the carbon pick-up success, a test with titanium-6Al-4Valloy is provided. When the binder composition of the present inventionis combined with a titanium-6Al-4V alloy to form the green composition,such as shown above in Example 12, the green composition has a carboncontent of approximately 10 wt %. The first step of debinding is carriedout at a temperature from about 140° C. to about 220° C. in air,followed by the higher temperature debinding, from about 220° C. toabout 320° C. in hydrogen. In duplicate tests, the measured carboncontent of the resulting parts was 0.02 wt % (200 ppm) and 0.025 wt %(250 ppm). When a conventional binder composition, includingpolypropylene, stearic acid and paraffin wax was employed in a paralleltest with titanium-6Al-4V, the initial carbon content of the greencomposition was substantially the same, i.e., approximately 10 wt %.This green composition was debound by conventional methods. The measuredcarbon content of the resulting parts was about 1.5 wt % (about 15,000ppm).

A wide variety of parts can be made by PIM in accordance with thepresent invention. Such parts include for example, for an inorganicpowder which is a metal, gun parts, shear clipper blades and guides,watch band parts, watch casings, coin feeder slots, router bits, drillbits, disk drive magnets, VCR recording heads, jet engine parts,orthodontic braces and prostheses, dental brackets, orthopedic implants,surgical tools and equipment, camera parts, computer parts, and jewelry.Such parts include for example, for intermetallic inorganic powders,turbochargers, high temperature insulators, spray nozzles and threadguides. Such parts include for example, for ceramic inorganic powders,optical cable ferrules, ski pole tips, hair cutting blades, airfoilcores, piezoelectric (e.g., lead zircon titanate, PZT) parts, oxygensensors and spray nozzles.

Binder Compositions for Press & Sinter Applications

The binder composition of the present invention may also be used forpress & sinter applications. In press & sinter application, theinorganic powder loading is considerably higher than in PIM. Thetrade-off for the higher loading is the limitation that the parts madeby a press & sinter process are quite limited in complexity. In fact,press & sinter can be considered to be limited to quite simple parts.The types of inorganic powders which can be used in press & sinterapplications are more limited, due to the requirement that the powdersbe sufficiently malleable and compactable to be useable in press &sinter applications. Powders having a high hardness value, such as forexample WC, are generally not useable in press & sinter applications.The hardness value becomes an issue in press & sinter applications dueto the low binder loadings used in press & sinter as compared to PIM.

In a press & sinter application, the loading of the binder compositionin the green composition is typically in the range from about 1% byvolume to about 10% by volume of the green composition from which thepart will be formed. (As with PIM applications, the green composition ismeasured on a volume basis, with the loadings expressed in volumepercentages.) In one embodiment, the loading of the binder compositionis 1% by volume, or 2% by volume, or 3% by volume, or 4% by volume. In apress & sinter process, the green composition is pressed into thedesired shape by means of, e.g., a hydraulic press. Once the part ispressed into its shape, it has a green strength in the range from about1,000 psi (about 70 Kg/cm²) to about 4,000 psi (about 281 Kg/cm²). Thepart is then sintered.

For a press & sinter application, the binder composition according tothe present invention has the following ranges of components (aspreviously, the binder composition is prepared on a weight by weightpercentage bases (wt %)).

aliphatic polyester polymer 10-50 wt % ethylenebisamide wax 30-70 wt %guanidine wetting agent 5-30 wt % additive 0.1-20 wt %

For press & sinter applications, the foregoing descriptions with respectto the selection of aliphatic polyester polymer, ethylenebisamide waxand guanidine wetting agent continue to apply. Thus, the acid used toform the reaction product of guanidine and acid is selected on the basisof the isoelectric point of the inorganic powder. Similarly, the samerange of inorganic powders can be used, as long as these are useable ina press & sinter application.

In view of the foregoing description, it is apparent that the presentinvention provides a new and improved binder which is formed and/or usedin accordance with a new and improved method. Although the invention hasbeen shown and described with respect to certain preferred embodiments,equivalent alterations and modifications will occur to others skilled inthe art upon reading and understanding this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described integers (components, compositions,steps, etc.), the terms used to describe such integers are intended tocorrespond, unless otherwise indicated, to any integer which performsthe specified function of the described integer (i.e., that isfunctionally equivalent), even though not structurally equivalent to thedisclosed structure which performs the function in the hereinillustrated exemplary embodiment or embodiments of the invention. Inaddition, while a particular feature of the invention may have beendescribed above with respect to only one of several illustratedembodiments, such feature may be combined with one or more otherfeatures of the other embodiments, as maybe desired and advantageous forany given or particular application.

1. A binder composition comprising: an aliphatic polyester polymer, anethylenebisamide wax; a guanidine wetting agent; and an additive whichis a debinding accelerator or debinding extender.
 2. The bindercomposition of claim 1, wherein the additive is a debinding acceleratorwhich accelerates debinding.
 3. The binder composition of claim 2,wherein the debinding accelerator is an organic peroxide.
 4. The bindercomposition of claim 3, wherein the organic peroxide is a dialkylperoxide.
 5. The binder composition of claim 3, wherein the organicperoxide is 2,5-dimethyl-2,5-di(t-butylperoxy)hexane.
 6. The bindercomposition of claim 1, wherein the guanidine wetting agent is presentin an amount from about 0.1 wt % to about 50 wt %, the aliphaticpolyester polymer is present in the range from about 20 wt % to about 75wt %, the ethylenebisamide wax is present in the range from about 15 wt% to about 40 wt %, and the debinding additive is present in the rangefrom about 0.01 wt % to about 25 wt %, each based oh the bindercomposition.
 7. The binder composition of claim 6, wherein the bindercomposition further comprises a plasticizer in an amount from about 0.01wt % to about 25 wt %.
 8. The binder composition of claim 2, wherein thedebinding accelerator is a metal.
 9. The binder composition of claim 2,wherein the debinding accelerator increases the rate at which thealiphatic polyester debinds during debinding of the binder composition.10. The binder composition of claim 2, wherein the debinding acceleratorcleaves the aliphatic polyester polymer into polymeric fragments. 11.The binder composition of claim 2, wherein the debinding accelerator ispresent in the range from about 0.01 wt % to about 10 wt % of the bindercomposition.
 12. The binder composition of claim 1, wherein the additiveis a debinding extender which extends debinding.
 13. The bindercomposition of claim 12, wherein the debinding extender is a polymerhaving a debinding temperature in the range from about 450° C. to about850° C.
 14. The binder composition of claim 12, wherein the debindingextender comprises at least one of polypropylenes or polymethacrylates.15. The binder composition of claim 12, wherein the debinding extenderis a polymer having a weight average molecular weight in the range fromabout 25,000 to about 250,000.
 16. The binder composition of claim 15,wherein the polymer has a weight average molecular weight in the rangefrom about 40,000 to about 120,000.
 17. The binder composition of claim14, wherein the polypropylene has a weight average molecular weight ofabout 50,000.
 18. The binder composition of claim 14, wherein thepolymethacrylate has a weight average molecular weight of about 100,000.19. The binder composition of claim 12, wherein the debinding extenderis present in the range from about 1 wt % to about 20 wt % of the bindercomposition.
 20. A green composition comprising the binder compositionof claim 1, and an inorganic powder selected from a metal powder, ametal oxide powder, an intermetallic powder and a ceramic powder. 21.The green composition of claim 20, wherein the binder composition ispresent in an amount in the range from about 30 vol % to about 60 vol %and the inorganic powder is present in an amount from about 70 vol % toabout 40 vol %.
 22. The green composition of claim 20, wherein thebinder composition is present in an amount in the range from about 1 vol% to about 10 vol % and the inorganic powder is present in an amountfrom about 99 vol % to about 90 vol %.
 23. A method for forming a partby powder injection molding, comprising: (a) forming a green compositioncomprising a binder composition and an inorganic powder, wherein thebinder composition comprises an aliphatic polyester polymer, anethylenebisamide wax, a guanidine wetting agent and an additive; and (b)healing the green composition to debind the green composition, whereinthe additive accelerates or extends step (b).
 24. The method of claim23, wherein the inorganic powder is selected from a metal powder, ametal oxide powder, an intermetallic powder and a ceramic powder. 25.The method of claim 23, wherein the additive is a debinding acceleratorwhich accelerates step (b).
 26. The method of claim 25, wherein thedebinding accelerator is an organic peroxide.
 27. The method of claim26, wherein the organic peroxide is a dialkyl peroxide.
 28. The methodof claim 23, wherein the additive is a debinding extender which extendsstep (b).
 29. The method of claim 28, wherein the debinding extender isa polymer having a debinding temperature in the range from about 450° C.to about 750° C.
 30. The method of claim 28, wherein the debindingextender is at least one of polypropylenes or polymethacrylates.
 31. Themethod of claim 30, wherein the polymer is a polypropylene having aweight average molecular weight from about 50,000 to about 100,000. 32.The method of claim 23, wherein step (a) further comprises addition of aplasticizer to the binder composition.
 33. The method of claim 23,wherein step (b) includes a plurality of temperature increases toelevated temperatures.
 34. The method of claim 33, wherein at least oneof the elevated temperatures is maintained substantially constant for aperiod of time.
 35. The method of claim 25, wherein the additive reducesthe time for debinding of the aliphatic polyester polymer.
 36. Themethod of claim 28, wherein the additive debinds at an elevatedtemperature which is higher than a temperature at which substantiallyall of said aliphatic polyester polymer, said ethylenebisamide wax, andsaid guanidine wetting agent have been debound.
 37. The method of claim23, further comprising a step of transferring the flowable greencomposition into a mold for a part.
 38. The method of claim 37, whereinstep (b) comprises healing the part to a temperature at which the bindercomposition debinds.
 39. The method of claim 38, further comprising astep of heating the part to a temperature at which the powder issintered.
 40. The method of claim 38 wherein step (b) occurs by reversedebinding\of the binder composition.
 41. The method of claim 23, whereinstep (b) comprises heating the green composition to a plurality ofelevated temperatures to debind the green composition by reversedebinding, wherein a first elevated temperature corresponds to thedebinding temperature of the aliphatic polyester polymer, a secondelevated temperature corresponds to the debinding temperature of boththe ethylenebisamide wax and the guanidine wetting agent.
 42. The methodof claim 41, wherein the additive is a debinding extender and step (b)further comprises heating to a further elevated temperature whichcorresponds to the debinding temperature of the debinding extender. 43.The method of claim 23 wherein step (b) occurs by reverse debinding ofthe binder composition.
 44. A binder composition comprising: analiphatic polyester polymer; an ethylenebisamide wax; and a guanidinewetting agent; with the proviso that the aliphatic polyester polymer isnot a poly(propylene) carbonate polyester polymer.
 45. The bindercomposition of claim 44, wherein the aliphatic polyester polymer is apolyester having the following general formula (A):

wherein R and R′ are independently a single bond or a C₁-C₁₀ saturatedor unsaturated aliphatic, straight chain, branched chain, cyclic oralicyclic group, which group may include one or more of —O—, —S—, —S—S—,—SO₂—, or —C(O)—; and n=about 50 to about 500, and wherein mixtures of Rand R′ may be included, to form copolyesters.


46. The binder composition of claim 44, wherein the aliphatic polyesterpolymer is a polyester having the following general formula (B):whereinR″ is a C₂-C₁₈ saturated or unsaturated aliphatic, straight chain,branched chain, cyclic or alicyclic group, which group may include oneor more of —O—, —S—, —S—S—, —S2-, or —C(O)—; and m=about 200 to about2000.
 47. The binder composition of claim 46, wherein the aliphaticpolyester polymer is polycaprolactone.
 48. The binder composition ofclaim 44, wherein the aliphatic polyester polymer is a polyester havingthe following general formula (C):

wherein R⁴ and R⁵ are independently a single bond or a C₁-C₁₀ saturatedor unsaturated aliphatic, straight chain, branched chain, cyclic oralicyclic group, which group may include one or more of —O—, —S—, —S—S—,—SO₂—, or —C(O)—; and X and Y are selected such that the total of X andY yields a polymer having a molecular weight in the range from about30,000 to about 180,000, wherein mixtures of R⁴ and R⁵ may be included,to form copolyesters, with the proviso that both of R⁴ and R⁵ are notpropylene.
 49. The binder composition of claim 44, wherein the guanidinewetting agent is present in an amount from about 10 wt % to about 50 wt%, the aliphatic polyester polymer in the range from about 20 wt % toabout 75 wt %, and the ethylenebisamide wax in the range from about 15wt % to about 40 wt %, each based on the binder composition.
 50. Thebinder composition of claim 44, wherein the guanidine wetting agent is amixture of guanidine stearate and guanidine 2-ethylhexanoate.